116 urn:lsid:arphahub.com:pub:619a5b3a-5ec8-5ff7-b0b1-5070a7c17694 urn:lsid:zoobank.org:pub:70C65CC0-001D-487B-A05D-B86A205B9582 Contributions to Entomology CTE 0005-805X 2511-6428 Senckenberg Gesellschaft für Naturforschung 10.3897/contrib.entomol.76.e189240 189240 Research Article Formicidae Hymenoptera Vespoidea Identification key Taxonomy A new species complex in the genus Camponotus Mayr, 1861 (Hymenoptera: Formicidae), with the description of a new species Chan Marco beeguy02@connect.hku.hk https://orcid.org/0009-0001-4459-3966 1 Hamer Matthew T. https://orcid.org/0000-0001-6728-9046 1 Guénard Benoit https://orcid.org/0000-0002-7144-1175 1 2 School of Biological Sciences, The University of Hong Kong, Pok Fu Lam Road, Hong Kong, Hong Kong SAR, China School of Biological Sciences, The University of Hong Kong Hong Kong China Hong Kong Biodiversity Museum, School of Biological Sciences, The University of Hong Kong, Hong Kong SAR, China Hong Kong Biodiversity Museum, School of Biological Sciences, The University of Hong Kong Hong Kong China

Corresponding author: Marco Chan (indonimus0702@gmail.com)

Academic editor: Brendon Boudinot

 2026 18 08 2026 76 1 139 158 439767E3-F0AD-57E3-8252-479FE6E86C8A 04810B1E-3838-4859-AB40-B044F129DE4B 20 02 2026 28 07 2026 Marco Chan, Matthew T. Hamer, Benoit Guénard This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. https://zoobank.org/04810B1E-3838-4859-AB40-B044F129DE4B

Orthonotomyrmex Ashmead, 1906 is one of the most morphologically distinct subgenera in the genus Camponotus Mayr, 1861 with a marginated propodeum, nodiform petiole and punctate sculpturing covering most of the body. Here, we propose a new species complex native to Southeast Asia, the Camponotus selene–complex. We also propose the elevation of Camponotus obtusatus (Emery, 1895) as a valid species, the synonymisation of C. lasiselenesyn. nov. with C. obtusatus and describe a new species, Camponotus orthogoniussp. nov. from Hong Kong SAR. The type series was collected within multiple neighbouring twigs from a singular fallen tree suggesting a polydomic colony structure. Keys to the known species of the selene–complex are provided for both minor and major workers. We also provide new distribution data for Camponotus obtusatusstat. nov. and Camponotus siamensis Jaitrong & Jeenthong, 2022 from Fujan Province, China and Laos, respectively. The proposal of the new selene–complex serves to facilitate future revisions Orthonotomyrmex when more Afrotropical specimens are available to better diagnose the subgenus. The discovery of C. orthogoniussp. nov., alongside newly–reported range extensions, reinforces the potential of further arboreal ant species discoveries in Southeast Asia.

 Arboreal carpenter ant dichotomous key new species range expansion taxonomy University of Hong Kong 501100003803 https://ror.org/02zhqgq86 http://doi.org/10.13039/501100003803 1. Research Grant Council of the Hong Kong Government, 2023/2024 General Research Fund project #17103223 and project #17121922 2. Lantau Conservation Fund RE-2021-14 Introduction

Camponotus Mayr, 1861 is a hyperdiverse ant genus consisting of 1100 extant species and 400 subspecies and one fossil species (Bolton 2026). Camponotus presents a global distribution, except in the United Kingdom and at very high latitudes (e.g. Greenland, Antarctica; Janicki et al. (2016); Guénard et al. (2017)). In China, 115 species and five subspecies have thus far been recorded (Ran and Zhou 2011; Guénard and Dunn 2012; Liu et al. 2020), with several potential unrecorded and undescribed species remaining (Liu et al. 2015, 2020).

Apart from some monomorphic species such as those from the subgenus Karavaievia Emery, 1925 (Emery 1925), members of the genus are usually polymorphic, with workers exhibiting both a minor and a major subcaste, sometimes with a median subcaste. The variation in body size can relate to task allocation within the colony, with smaller minor workers helping with tasks such as foraging and brood care, while the larger major workers help to defend the colony against intruders using their larger heads and mandibles, alongside blocking nest entrances during an attack (Busher et al. 1985; Rossi and Feldhaar 2021; Kawamoto et al. 2025). High degrees of polymorphism, along with globally scattered type specimens from Asia, have resulted in numerous misidentifications within the genus and confusion with other genera such as Colobopsis Mayr, 1861 (Ward and Boudinot 2021). As a result, Camponotus is considered by myrmecologists as a challenging group to identify and work on (Ward et al. 2016; Ward and Boudinot 2021; Ye et al. 2025). Camponotus is grouped into 41 subgenera (Bolton 2026), although this will likely be changed as many are non–monophyletic (Ward et al. 2025). The subgenus Orthonotomyrmex Ashmead, 1906 is one of the most morphologically distinct. Members differs from their congeners by having a marginated propodeum, a nodiform petiole and punctate sculpturing (Emery 1925). First proposed by Ashmead (1905) as Orthonotus Ashmead, 1905, the name was soon changed due to its homonymy with a hemipteran species (Stephens 1829; Ashmead 1906). Orthonotomyrmex currently comprises of 19 valid species (Bolton 2026), distributed in the Afrotropics, Arabian Peninsula and Southeast Asia (Arnold 1917; Wheeler 1922; Wang and Wu 1994; Subedi et al. 2021; Jaitrong and Jeenthong 2022). Eight species have been recorded throughout Southeast Asia (Stitz 1938; Wang and Wu 1994; Subedi et al. 2021), of which three species, C. lasiselene Wang & Wu, 1994 syn. nov., C. selene (Emery, 1889) and C. yiningensis Wang & Wu, 1994 are recorded in China (Wang and Wu 1994; Guénard and Dunn 2012).

Closer inspection of specimens, however, revealed inconsistent morphologies between Orthonotomyrmex species: within the eight Southeast Asian species, some possess a marginated pronotum with humeral corners and a bilobed or right–angled propodeum such as C. impressilabris Stitz, 1938 and C. obtusatus stat. nov., but are absent in other regional congeners such as C. multilarius Emery, 1893, C. wasmanni Emery, 1893 and C. yiningensis. The right–angled propodeum, however, can be observed in some Afrotropical and West Asian species such as C. opaciventris Mayr, 1879 and C. sericeus (Fabricius, 1798). One possible reason for the differences observed may be attributed to allopatric speciation occurring in Afrotropical and Indomalayan populations. Recent phylogenetic evidence revealed that members within the subgenus belong to two sister clades, with the type species C. sericeus placed in the Afrotropical sericeus clade and C. multilarius in the Afrotropical–Indomalayan C. maculatus (Fabricius, 1782) clade (Ward et al. 2025), which further blurs the taxonomy of the subgenus.

In this paper, we introduce a new species complex in the subgenus Orthonotomyrmex superficially similar to the type species C. sericeus, henceforth named the selene–complex, based on the earliest described species C. selene, taking into consideration the distinct morphology of the workers. Along with providing images of the holotype worker specimen of C. lasiselene syn. nov., we propose the synonymy of C. lasiselene syn. nov. with C. selene obtusatus (Emery, 1895) and raise the latter to species rank as C. obtusatus (Emery, 1895), stat. nov. We also describe a new species in the selene–complex, Camponotus orthogonius sp. nov. from southern China and provide ecological notes. The morphological descriptions of the minor and major workers are described in detail coupled with high resolution photographs. Comparative notes are also given against similar species recorded in China and Southeast Asia and keys to the species in the selene–complex are provided. We also report new locality records for C. obtusatus and C. siamensis Jaitrong & Jeenthong, 2022, for which we provide high resolution photographs of the median worker of C. siamensis.

 Materials and methods

Specimens were collected across Hong Kong, including on Lantau Island and the New Territories, as well as provinces in mainland China (Fujian, Guangdong, Guangxi, Hainan), Laos and Thailand. All specimens were preserved in 75% or 95% ethanol before pin–mounting. Specimens were imaged through focus–stacking using the Leica M205 C Stereomicroscope with a DMC5400 Camera in LASX software (v.3.7.4.23463). Images and image plates were then edited in Adobe Photoshop. Images of the holotype worker specimen of C. lasiselene syn. nov. provided by Professor Zheng Hui Xu were used to compare against the new species.

All measurements were taken using a Leica M205 C Stereomicroscope and the Leica Application Suite v.4.5 programme, with all values measured in millimetres and rounded off to two decimal places. The traits measured in this paper utilise those generally adopted by other taxonomic studies (e.g. Jaitrong and Jeenthong (2022); Ward et al. (2025)), including:

Head length (HL) Maximum length of head, measuring from anterior margin of clypeus to posterior margin of head in full face view;

Head width (HW) Maximum width of head measuring from lateral margins in full face view excluding the eyes;

Eye length (EL) Maximum length of eye in oblique lateral view;

Eye width (EW) Maximum width of eye in oblique lateral view;

Scape length (SL) Maximum length of the antennal scape, not including the basal neck and condylar club, measured from full face view;

Clypeus length (CL) Maximum length of clypeus measured from the anterior margin to posterior margin across the mid–line in anterodorsal view;

Clypeus width (CW) Maximum width of clypeus measured between each lateral margin in full face view;

Mandible length (MaL) Maximum length of mandible measured from tip of apical tooth to posterior of external mandibular margin in oblique lateral view;

Weber’s Length (WL) Maximum length of mesosoma measured from anterior pronotum margin (excluding the pronotal collar) to the posteroventral extremity of the metapleuron in lateral view;

Petiole height (PH) Maximum height of the petiole in lateral view from the ventral most margin of subpetiolar process to the apex of the petiole;

Petiole length (PL) Maximum anteroposterior length of the petiole in lateral view, perpendicular to line measuring petiole height;

Hind femur length (HFL) Maximum length of the hind femur from base to apex;

Cephalic index (CI)HW / HL × 100;

Eye index (EI)EL / HW × 100;

Scape index (SI)SL / HW × 100;

Femur index (FeI)HFL / HW × 100.

The following abbreviations for depository institutions are used in this study:

CAFB Chinese Academy of Forestry, Beijing, China;

HKBM Hong Kong Biodiversity Museum, The University of Hong Kong, Hong Kong;

IBBL Insect Biodiversity and Biogeography Laboratory, The University of Hong Kong, Hong Kong;

THNHM Natural History Museum of the National Science Museum, Thailand;

ZRC Zoological Reference Collection, Lee Kong Chian Natural History Museum, Singapore.

 Results <italic><tp:taxon-name><tp:taxon-name-part taxon-name-part-type="genus" reg="Camponotus">Camponotus</tp:taxon-name-part> <tp:taxon-name-part taxon-name-part-type="species" reg="selene">selene</tp:taxon-name-part></tp:taxon-name></italic>–complex

Camponotus impressilabris Stitz, 1938.

Camponotus obtusatus (Emery, 1895), stat. nov.

Camponotus lasiselene Wang & Wu, 1994, syn. nov.

Camponotus orthogonius sp. nov.

Camponotus selene (Emery, 1889).

Camponotus siamensis Jaitrong & Jeenthong, 2022.

Diagnosis of the <italic>selene</italic>–complex

Small to medium–sized workers. Head of major workers longer than wide, clypeus truncated; Head with areolate–rugose sculpturing. In lateral view, propodeum at a right angle or bidentate, forming propodeal spines. In dorsal view, pronotum marginate, forming sharp or blunt–edged humeral corners; mesosoma trapezoidal in shape. Mesosoma dorsum with abundant short, erect, fine to stout hairs. The distribution is currently confined to the Indomalaya Region unlike other current Orthonotomyrmex species whose distribution extends from Asia to the Afrotropics.

The selene–complex shares a resemblance with other Orthonotomyrmex species by possessing a right–angled propodeum in lateral view, but overall can be distinguished by the smaller–sized workers, presence of sparse short stout hair across the body and the head of major workers longer than wide instead of wider than long and possessing a truncated clypeus, resulting in a phragmotic head (see Table 1). Furthermore, the marginate pronotum with distinct humeral corners is a unique character that alone differentiates members of the selene–complex from other Orthonotomyrmex species, except for C. multilarius Emery, 1893 and C. wasmanni Emery, 1893. Members of the selene–complex are typically much smaller than the latter two species (e.g. WL of C. orthogonius = 1.46–2.18; WL of C. multilarius = 2.4–3.1; Wachkoo (2015)) and overall can be distinguished by the right–angled or bidentate propodeum in lateral view instead of roundly convex and short stout hairs sparsely distributed across the body, instead of dense, long, fine hairs. Along with morphological differences listed in Table 1, minor workers of the selene–complex can be further distinguished from C. multilarius and C. wasmanni by the following characters: in full–face view, clypeus wider than long instead of longer than wide, head with areolate–rugulose sculpturing instead of microreticulate. Major workers of the selene–complex can be differentiated from those of C. multilarius by possessing a bicoloured head (dark–grey and orange), instead of uniform in colour (dark–grey) (the major worker of C. wasmanni has yet to be formally described, but is here assumed to be similar to C. multilarius).

Diagnostic characters of the selene–complex in comparison with other Orthonotomyrmex species.

Caste selene–complex Other Orthonotomyrmex species
Minor worker Head as long as wide Head longer than wide
Pronotum marginate Pronotum not marginate
Pronotum with humeral corners Pronotum without humeral corners
Mesosoma dorsum outline straight to narrowly convex Mesosoma dorsum outline distinctly convex
Short stout hairs sparsely distributed across the body Long fine hairs densely distributed across the body
Major worker Head longer than wide Head wider than long
Lateral margins of head straight to subtly convex Lateral margins of head roundly convex
Posterior margin of head straight Posterior margins of head concave
Genae prominent Genae not prominent
Clypeus truncated Clypeus not truncated
Mesosoma dorsum outline continuous Mesosoma dorsum outline not continuous, interrupted by metanotal groove
Mesosoma dorsum outline subtly convex Mesosoma dorsum outline roundly convex
Short stout hairs sparsely distributed across the body Long fine hairs densely distributed across the body

The selene–complex is similar to species in the subgenus Myrmamblys Forel, 1912 in that the major workers have heads longer than they are wide, a truncated clypeus and prominent genae in full face view, but differ by both minor and major workers possessing flat and marginated propodeum dorsum in lateral view instead of saddle–shaped, a wide petiolar node, instead of thin and the marginate pronotum with distinct humeral corners in dorsal view, instead of convex.

Animalia Hymenoptera Formicidae D50286E8-4DB8-50DA-B0D0-5649EF303C00 Camponotus obtusatus (Emery, 1895) stat. nov. Camponotus selene obtusatus (Emery, 1895). Polyrhachis selene subsp. obtusata Emery, 1895 m: 480 (w.) Myanmar. (images examined) Combination in Camponotus: Emery, 1896j: 376. Combination in Camponotus (Orthonotomyrmex): Emery, 1925d: 125. Subspecies of Camponotus selene: Forel, 1895: 456; Emery 1896: 376 (in list); Bingham 1903: 409; Chapman and Capco 1951: 242; Bolton 1995: 115; Dorow 1995: 65; Bharti et al. 2016: 26. Animalia Hymenoptera Formicidae A785EBA8-49C8-5C7A-BA8D-5600E82023DE Camponotus lasiselene Wang & Wu, 1994. syn. nov. Figs 1 , 2 , 3 Camponotus lasiselene Wang & Wu, 1994: 24, fig. 3 (w.) China (Yunnan Province) (images examined). Combination in Camponotus (Orthonotomyrmex): Radchenko, 1997d: 812. Material examined.

Thailand — E Thailand; Chanthaburi Prov. • 1 minor worker; Pong Nam Ron District; 13.v.2008; W. Jaitrong leg.; WJT08–E027; THNHM–I–24820; THNHM (images examined) • 1 major worker; As previous; THNHM–I–24822; THNHM (images examined) — Chiang Mai • 1 minor worker; Mae Sae; 19.2434°N, 98.6548°E; ± 250 m2; 969 m a.s.l.; 5.viii.2024; gen. forager; M. T. Hamer; MTH1371; THNHM • 1 minor worker; Mae Sae; 19.238938°N, 98.652248°E; ± 20 m2; 1077 m a.s.l.; 10.viii.2024; gen. forager; M. T. Hamer leg.; MTH1268; ANTWEB1011370; THNHM • 1 minor worker; As previous; IBBL • 1 minor worker; Mae Sae; 19.2434°N, 98.6548°E; ± 250 m2; 969 m a.s.l.; 11.viii.2024; gen. forager; M. T. Hamer leg.; MTH1392; ANTWEB1011187; IBBL • 1 minor worker; As previous; 11–14.viii.2024; gen. forager; M. T. Hamer leg.; MTH1331; THNHM.

10.3897/contrib.entomol.76.e189240.figure1 F3CBD3C3-E0D0-5C98-B481-53CF411706F1

Camponotus lasiselene syn. nov. holotype specimen from Yunnan Province, China. A. Head in full–face view; B. Body in lateral view; C. Body in dorsal view; D. Holotype specimen label. Photos were imaged by Dr. Zhi–Lin Chen and Dr. Xin–Min Zhang and provided by Professor Zheng–Hui Xu. Scale bars were added using ImageJ.

https://binary.pensoft.net/fig/1748346 10.3897/contrib.entomol.76.e189240.figure2 CEDC83CA-89AB-50A0-9F8E-9025F0B38AD0

Camponotus selene obtusatus syntype minor worker (CASENT0905416, photographer Ziv Lieberman). A. Head in full–face view; B. Body in lateral view; C. Body in dorsal view. Images available from http://www.antweb.org.

https://binary.pensoft.net/fig/1748347 10.3897/contrib.entomol.76.e189240.figure3 A201EF16-128D-57B1-86DB-59316470242F

Camponotus obtusatus stat. nov. non–type specimens from Fujian Province, China (ANTWEB1011185; A, C, E) and Chiang Mai, Thailand (ANTWEB1011370; B, D, F). A, B. Head in full–face view; C, D. Body in lateral view; E, F. Body in dorsal view.

https://binary.pensoft.net/fig/1748348

China — Guangdong Prov. • 1 minor worker; Xidamingshan; 15.x.1998; J. R. Fellowes leg.; ANTWEB1015825; MBS006294; HKBM • 1 minor worker; Diding Headwater Forest Nature Reserve; 1150 m a.s.l.; 9.vii.1999; J. R. Fellowes leg.; MBS013104; HKBM • 1 minor worker; As previous; MBS013230; HKBM — Guangxi Prov. • 1 minor worker; Nonghua; 980 m a.s.l.; 13.vii.1999; J. R. Fellowes leg.; MBS013112; HKBM — Fujian Prov. • 1 minor worker; Huangchulin NR; 26.32779°N, 118.72156°E; ± 20 m2; 301 m a.s.l.; 16.vi.2023; LLex.r12; L. Xuan leg.; HCL–EU–r12–W1–27; ANTWEB1011185; IBBL • 1 minor worker; As previous; ANTWEB1011186; IBBL.

 Distribution.

Camponotus obtusatus stat. nov. is recorded in Fujian Province, China for the first time, presenting the easternmost distribution for the species, completing its previous known distribution in Myanmar and Assam State (India). The species has been previously recorded in other provinces in mainland China (Guangdong, Guangxi, Hunan, Xizang, Yunnan) Nepal, Thailand and Vietnam (Zhou 2001; Yamane et al. 2002; Zhao et al. 2009; Zhang et al. 2012; Janicki et al. 2016; Guénard et al. 2017; Liu et al. 2020; Subedi et al. 2021; Jaitrong and Jeenthong 2022).

 Ecology.

Two minor workers were collected from Huangchulin Nature Reserve, Fujian Province, within randomly collected leaf litter from a Eucalyptus plantation and extracted with a Winkler extractor over 72 hours. Solitary foraging workers were collected by hand on ornamental plants in a garden in Chiang Mai, Thailand.

 Comments.

In the description of C. lasiselene syn. nov., the authors distinguished it from C. selene, but did not compare it against the subspecies C. selene obtusatus. We note several morphological similarities between the holotype specimen of C. lasiselene syn. nov. and the syntype specimen of C. selene obtusatus: in full–face view, head is trapezoidal in shape with angulate posterolateral corners (Figs 1A, 2A); in lateral view, the petiolar node is subrectangular with a flat apex and the metasoma has dense punctate sculpturing (Figs 1B, 2B); in dorsal view, anterior pronotal margin has only one concavity on each side (Figs 1C, 2C). Such similarities are consistent when examining images of the syntype worker and newly–collected specimens from the mainland China and Thailand, though there is some variation in the presence of acute humeral corners on the pronotal margin in dorsal view between individuals from the two localities (Fig. 3E, F). On the other hand, C. selene differs from C. selene obtusatus by the following: in full–face view, posterolateral corners rounded (Figs 2A, 11A); in lateral view, the petiolar node is subrectangular with a triangular apex and the metasoma is smooth and shiny (Figs 2B, 11B); in dorsal view, anterior pronotal margins with two concavities on each side (Figs 2C, 11C). While we were unsuccessful in obtaining the syntype specimen of C. selene obtusatus for physical examination from Museo Civico di Storia Naturale, Italy, considering the distinctiveness of C. selene obtusatus compared to C. selene and the close morphological similarity of C. lasiselene syn. nov. with C. selene obtusatus, there is sufficient evidence to raise C. selene obtusatus to species rank, henceforth referred to as C. obtusatus stat. nov. and consider C. lasiselene syn. nov. as a junior synonym of C. obtusatus stat. nov.

Several studies (Wang and Wu 1994; Subedi et al. 2021; Jaitrong and Jeenthong 2022) have noted that C. obtusatus stat. nov. and C. selene are morphologically similar and only differ by the density of the pilosity. Pilosity, however, can be lost due to abrasion as we have observed in newly–collected specimens. Therefore, we believe that pilosity is not a consistent character to differentiate the two species and the aforementioned morphological differences between C. selene and C. obtusatus stat. nov. that we have observed are sufficient and more reliable to differentiate the two species.

Closer examination of minor workers collected from Fujian Province, China and Chiang Mai, Thailand revealed only subtle variations. The minor workers from Fujian differ from those in Thailand by the following: in lateral view, humeral corners of pronotums are less pronounced and not forming acute triangular corners, petiolar node taller than long; in dorsal view (Fig. 3). However, the variation in the shape of the petiole was also observed between specimens from the same locality in Thailand. Otherwise, all other morphological characteristics correspond to C. obtusatus stat. nov.

No major workers of C. obtusatus stat. nov. were described previously or collected in this study. Two previous studies have collected and identified major workers of this species in Yunnan Province, China and Thailand (Liu et al. 2020; Jaitrong and Jeenthong 2022), but there are some notable characters that differentiate the Yunnan specimens from the Thailand specimens: in full–face view, frontal carina more sharply convex rather than moderately convex; in lateral view, apex of petiolar node marginated instead of roundly convex; in dorsal view, propodeal spines form two rounded hooks instead of two straight spines. The minor workers from both studies correspond to C. obtusatus stat. nov.

 Animalia Hymenoptera Formicidae DC9F2344-0ED8-5B37-ACDC-7941ECA7662B Camponotus orthogonius https://zoobank.org/98EF5757-BE45-4CAF-962B-65B3F2DA0168 Chan, Hamer & Guénard sp. nov. Figs 4 , 5 , 6A, C, E Type material.

Holotype worker. China — Hong Kong SAR • minor worker; Tai Lam; Tsing Tam Village; 22.4255026°N, 114.097303°E; ± 50 m2; 102 m a.s.l.; 2.iv.2025; M. Chan & Y. H. Wu leg.; Hand coll.; Secondary forest; MCHC051–23; ANTWEB1010678; ZRC.

10.3897/contrib.entomol.76.e189240.figure4 3EDDC391-4C33-5B3C-9F0F-216A47DF714E

Camponotus orthogonius sp. nov. holotype minor worker (ANTWEB1010678). A. Head in full–face view; B. Body in lateral view; C. Body in dorsal view.

https://binary.pensoft.net/fig/1748349 10.3897/contrib.entomol.76.e189240.figure5 17CE25DA-2391-50DF-9B67-9D4D35EE62CE

Camponotus orthogonius sp. nov. paratype major worker (ANTWEB1010676). A. Head in full–face view; B. Body in lateral view; C. Body in dorsal view.

https://binary.pensoft.net/fig/1748350 10.3897/contrib.entomol.76.e189240.figure6 A3614396-AAE7-5061-8493-1FA7565CA52F

Camponotus orthogonius sp. nov. (ANTWEB1012837) (A, C, E) and Camponotus siamensis (MBS013226) (B, D, F) non–type minor worker specimens from Hainan Province, China. A, B. Head in full–face view; C, D. Body in lateral view; E, F. Body in dorsal view.

https://binary.pensoft.net/fig/1748351 Paratype workers.

China — Hong Kong SAR • 1 major worker; same as holotype; MCHC051–01; ANTWEB1010676; IBBL • 1 major worker; As previous; MCHC051–02; ANTWEB1010690; HKBM • 1 major worker; As previous; MCHC051–03; ANTWEB1010691; THNHM • 1 minor worker; As previous; MCHC051–04; ANTWEB1011150; IBBL • 1 minor worker; As previous; MCHC051–11; ANTWEB1011151; IBBL • 1 minor worker; As previous; MCHC051–13; ANTWEB1011152; IBBL • 1 major worker; As previous; MCHC051–21; ANTWEB1010677; ZRC • 1 minor worker; As previous; MCHC051–22; ANTWEB1010680; HKBM • 1 minor worker; As previous; MCHC051–24; ANTWEB1010679; ZRC • 1 minor worker; As previous; MCHC051–25; ANTWEB1011153; IBBL • 1 minor worker; As previous; MCHC051–30; ANTWEB1011154; IBBL • 1 minor worker; As previous; MCHC051–031; ANTWEB1011155; IBBL • 1 minor worker; As previous; MCHC051–32; ANTWEB1010681; THNHM.

 Additional material examined.

China — Hong Kong SAR • 1 minor worker; Lantau; Butterfly Hill; 7.x.1996; J. R. Fellowes leg.; ANTWEB1015823; MBS006292; HKBM • As previous; MBS013217; HKBM • 1 minor worker; Lantau; Shui Hau; 22.22032°N, 113.9137°E; ± 50 m2; 55 m a.s.l.; 31.viii.2023; M. T. Hamer leg.; Hand coll.; MTH255; IBBL • 1 minor worker; Tai Mo Shan; Kap Lung Forest Trail; 22.41088°N, 114.1045°E; ± 50 m2; 450 m a.s.l.; 17.ix.2023; M. T. Hamer leg.; Hand coll.; MTH445; IBBL • 1 minor worker; Lantau; San Tau Village; 22.28578°N, 113.9243°E; ± 20 m2; 10 m a.s.l.; 20.ix.2023; M. T. Hamer leg; gen. forager; MTH491; IBBL • 1 minor worker; As previous; ANTWEB1010453; IBBL • 1 minor worker; As previous; ANTWEB1010454; IBBL • 1 major worker; As previous; ANTWEB1010456; IBBL • 5 minor workers; Lantau; San Tau Village; 22.42784°N, 114.1779°E; ± 20 m2; 10 m a.s.l.; 20.ix.2023; M. T. Hamer leg.; Hand coll.; MTH475; IBBL • 5 minor workers and 1 major worker; Lantau; San Tau Village; 22.2858°N, 113.9243°E; ± 20 m2; 10 m a.s.l.; 20.ix.2023; M. T. Hamer leg.; gen. forager; MTH429; IBBL • 3 minor workers; Lantau; San Tau Village; 22.28459°N, 113.9258°E; ± 20 m2; 10 m a.s.l.; 20.ix.2023; M. T. Hamer leg.; Hand coll.; MTH425; IBBL • 1 minor worker; Lantau; San Tau Village; 22.27853°N, 113.9311°E; ± 20 m2; 10 m a.s.l.; 20.ix.2023; M. T. Hamer leg.; Hand coll.; MTH461; IBBL • 3 minor workers; Lantau; San Tau Village; 22.28078°N, 113.9274°E; ± 20 m2; 10 m a.s.l.; 20.ix.2023; M. T. Hamer leg.; Hand coll.; MTH493; IBBL • 7 minor workers; Lantau; San Tau Village; 22.28765°N, 113.9222°E; ± 20 m2; 10 m a.s.l.; 20.ix.2023; M. T. Hamer leg.; Hand coll.; MTH476; IBBL • 2 minor workers; Lantau; San Tau Village; 22.28538°N, 113.9249°E; ± 20 m2; 10 m a.s.l.; 20.ix.2023; M. T. Hamer leg.; Hand coll.; MTH421; IBBL • 2 minor workers Lantau; San Tau Village; 22.28269°N, 113.9272°E; ± 20 m2; 10 m a.s.l.; 20.ix.2023; M. T. Hamer leg.; Hand coll.; MTH477; IBBL • 1 minor worker; Lantau; Shing Fai Orchard; 22.2441°N, 113.8845°E; ± 50 m2; 178 m a.s.l.; 5.x.2023; M. T. Hamer leg.; Hand coll.; MTH643; IBBL • 12 minor workers; Lantau; San Tau Village; 22.28422°N, 113.9259°E; ± 500 m2; 5 m a.s.l.; 16.x.2023; M. T. Hamer leg.; Hand coll.; MTH676; IBBL • 1 minor worker; Lantau; San Tau Village; 22.28656°N, 113.918381°E; ± 50 m2; 30 m a.s.l.; 16.x.2023; M. T. Hamer et al. leg.; Vegetation beating; STV–VBI–3; ANTWEB1010426; IBBL • 2 minor workers; Lantau; Pok Mong Village; 22.29836°N, 113.9719°E; ± 300 m2; 10 m a.s.l.; 6.v.2024; M. T. Hamer leg.; Hand coll.; MTH1088; IBBL • 1 minor worker; As previous; MTH1102; IBBL • 1 minor worker and 1 major worker; Tai Lam; Tsing Tam Village; 22.4199°N, 114.090684°E; ± 50 m2; 98 m a.s.l.; 18.i.2025; Y. H. Wu leg.; Hand coll.; LT051; IBBL • 1 major worker; Lantau; Tung O Ancient Trail; 22.278047°N, 113.891491°E; ± 50 m2; 27 m a.s.l.; 19.i.2025; M. Chan leg.; Hand coll.; MCHC037; IBBL • 2 minor workers and 1 major worker; Tai Lam; Tsing Tam Village; 22.4199°N, 114.090684°E; ± 50 m2; 98 m a.s.l.; 28.ii.2025; M. Chan & Y. H. Wu leg.; Hand coll.; MCHC050; IBBL • 1 minor worker; Lantau; Tai O Ancient Trail; 22.284946°N, 113.925337°E; ± 50 m2; 15 m a.s.l.; 11.iii.2025; B. W. Heath leg.; Hand coll.; MCHC052; IBBL • 63 minor workers and 9 major workers; same as holotype; MCHC051; IBBL — Hainan Prov. • 1 minor worker; Simaling Ecological Park; 18.30511°N, 109.5949°E; ± 4 m2; 40.1 m a.s.l.; 4.vi.2025; J. A. Siddiqui leg.; gen. coll.; HA57–2–CTMIN; ANTWEB1012837; IBBL • 3 minor workers; As previous; HA57–2; IBBL — Hong Kong SAR • 1 minor worker; Aberdeen; Aberdeen Country Park; 22.254184°N, 114.160469°E; ± 20 m2; 152 m a.s.l.; 10.xi.2025; M. Chan leg.; Hand Coll.; Secondary forest; MCHC251; IBBL.

 Minor worker

(Fig. 4). Diagnosis. Mediumsized workers (WL 1.46–1.87). Head length subequal to width (CI 93–100). With head in full–face view, antennal scape extending beyond occipital corner by ⅖ of its length. In lateral view, mesosoma dorsal outline nearly continuous and convex, only broken by metanotal groove; propodeal declivity concave, angle between declivity and dorsum forming a right angle. In dorsal view, anterior margin of pronotum convex, anterolateral margins sharply rounded.

 Measurements.

Holotype: HL 1.18; HW 1.18; EL 0.37; EW 0.28; SL 1.17; CL 0.34; CW 0.52; MaL 0.46; WL 1.59; PH 0.41; PL 0.32; HFL 1.15; CI 100; EI 32; SI 99; FeI 97.

Paratypes (n = 9): HL 1.13–1.47; HW 1.12–1.37; EL 0.35–0.41; EW 0.27–0.31; SL 1.15–1.23; CL 0.31–0.47; CW 0.51–0.56; MaL 0.44–0.53; WL 1.6–1.87; PH 0.37–0.46; PL 0.33–0.42; HFL 1.12–1.33; CI 84–99; EI 28–32; SI 84–103; FeI 88–100.

Non–types (n = 19): HL 1.08–1.34; HW 1.05–1.37; EL 0.33–0.4; EW 0.26–0.31; SL 1.13–1.24; CL 0.3–0.43; CW 0.49–0.56; MaL 0.42–0.52; WL 1.46–1.82; PH 0.34–0.45; PL 0.29–0.39; HFL 1.06–1.59; CI 93–100; EI 29–33; SI 90–109; FeI 92–119.

Head: Head slightly longer than wide (CI 93–100). With head in full–face view, posterolateral corners broadly rounded. Eye elliptical, longer than wide, touching lateral margins of head, slightly protruding from head capsule in dorsal view. Mandible subtriangular, lateral margins convex, masticatory margin with five teeth including apical tooth; apical and pre–apical teeth larger than preceding teeth. Clypeus subtrapezoidal, longer than wide, anterior margin convex, posterior margin emarginate. Frontal carina short and slightly convex, fading just after anteriormost margin of eye. Frontal triangle small, anterior margin convex, lateral margins close to straight. Antenna with 12 segments, funicular segments trapezoidal. Antennal scape longer than head length, extending slightly beyond posterior margins by ⅖ its length; funicular segment II slightly longer than funicular segments III and IV; funicular segments II to XI equal in length; funicular segment XI slightly longer than funicular segment X.

Mesosoma: In lateral view, mesosoma dorsal outline convex; humeral corners of pronotum distinct; promesonotal suture and metanotal groove distinct; mesopleuron, metapleuron and propodeal pleuron undivided by sulcus. Dorsal outline of propodeum straight and flat. Propodeal declivity concave, forming a right angle with propodeal dorsum. In dorsal view, anterior margin of pronotum weakly extending medially; humeral corner of pronotum blunt, forming a right angle; promesonotal suture outline sharply rounded; metanotal groove outline straight; promesonotum trapezoidal, widest at humeral corner of pronotum and narrowest at the posterior margins of the propodeum; pronotum, mesonotum and propodeum trapezoidal and collectively narrowing posteriorly.

Metasoma: In lateral view, petiolar node higher than long, narrowly elliptical and weakly inclining anteriorly; anterior and posterior faces weakly convex; apex of petiole roundly convex; subpetiolar process absent in lateral view. Abdominal tergites III–VII subequal in length. In dorsal view, petiolar node broader than long and narrowly elliptical.

Sculpturing: Entire head, mesosoma and metasoma covered with fine punctate sculpturing. Mandible sparsely punctate. Sculpturing on propodeum grades from punctate to areolate–rugose on propodeal declivity. Petiole with substrigulate sculpturing in lateral view, while punctate at its apex in dorsal view.

Pilosity: Body surface with sparse erect to suberect hairs and abundant depressed pubescence. Stout hairs present on vertex of head, promesonotum, posterior dorsum of propodeum, apex of petiolar node and anterior face of abdominal tergite III. Scapes and tibiae with dense depressed pubescence, without any standing hairs. Orifice without any radial hairs.

Colouration: Head, mesosoma and abdomen dark grey in colour. Mandible and antennal scape dark brown. Coxa black–grey; trochanter femur and tibia dark–brown; tarsus orange.

 Major worker

(Fig. 5). Diagnosis. Medium–sized workers (WL 1.99–2.18). Head subrectangular, longer than wide (CI 84–86). With head in full–face view, antennal scape of medium length, touching posterior margin of head; head bicoloured, anterior clypeal margin to the antennal insertion orange, antennal scrobe to the occipital corners black. In lateral view, mesosoma dorsum outline weakly convex; metanotal groove shallow; propodeal declivity concave, forming a right angle with dorsum of propodeum. In dorsal view, anterior pronotum margin weakly extending medially, humeral corners of pronotum bluntly angled; promesonotal suture slightly impressed; metanotal groove moderately impressed.

 Measurements.

Paratypes (n = 4): HL 1.83–2.02; HW 1.58–1.7; EL 0.43–0.47; EW 0.33–0.36; SL 1.14–1.26; CL 0.66–0.8; CW 0.58–0.64; MaL 0.61–0.68; WL 1.99–2.18; PH 0.48–0.57; PL 0.38–0.42; HFL 1.25–1.3; CI 84–86; EI 27–28; SI 68–76; FeI 74–79.

Head: Head rectangular in shape, longer than wide (CI 84–86). With head in full–face view, lateral margins of head weakly convex and parallel, posterior margin straight; posterolateral corners of head narrowly angled; posterior margin straight. Anterior third of head dorsum obliquely truncated and slightly concave in lateral view. Eye longer than wide, elliptical in shape. Mandible subtriangular, with five teeth on masticatory margin, including apical tooth. Clypeus subrectangular, slightly longer than wide; anterior and anterolateral margin of clypeus weakly concave and divided by a blunt angle, lateral margins weakly convex; median clypeal carina present and well impressed, shorter than frontal carina. Anterior margin of head surpassing clypeus, forming prominent genae. Frontal carina convex, diverging first and then converging posteriorly, almost reaching posterior margin of eye. Frontal triangle extremely small, anterior margin convex, while lateral margin weakly concave. Antennal scrobe mostly exposed, narrowly covered by frontal carina. Antenna with 12 funicular segments, antennal scape shorter than head length, just touching posterior margins of head. Funicular segments trapezoidal in shape; pedicel slightly longer than funicular segments II and III; funicular segments II–X equal in length; funicular segment XI slightly longer than funicular segment X.

Mesosoma: In lateral view, dorsal outline of mesosoma weakly convex; pronotal margin grading from sharp to soft–edged; promesonotal suture shallowly impressed; metanotal groove moderately narrowly impressed; propodeal margin dorsum straight, forming a right angle with the declivity, the latter deeply concave; mesopleuron, metapleuron and propodeal pleuron undivided by sulcus. In dorsal view, mesosoma trapezoidal, narrowing posteriorly; humeral corners of pronotum bluntly angled; promesonotal suture broadly round; metanotal groove outline transverse; posterior margin of propodeum subtly rounded; pronotum, mesonotum and propodeum all subtrapezoidal and narrowing posteriorly.

Metasoma: In lateral view, petiolar node roughly conical, longer than high and weakly inclining anteriorly; anterior face weakly convex, posterior face moderately convex; apex of petiolar node roundly convex; subpetiolar process absent; abdominal tergite III shorter than IV and V. In dorsal view, petiolar node wider than long and narrowly elliptical.

Sculpturing: Head and mesosoma densely, finely and uniformly punctate. With head in full–face view, anterior portion of head densely coarsely punctate with interface reticulate; mandibles sparsely coarsely punctate. Face of propodeal declivity punctate to areolate–rugulose. Petiole substrigulate. Abdominal tergites III to VII finely punctate, with anterior sections between abdominal segment III, IV and V substrigulate.

Pilosity: Head, mesosoma and abdomen with sparse erect to suberect hairs and abundant depressed pubescence. Stout hairs present on lateral margins and dorsum of head, mandibles, posterior dorsum of propodeum, apex of petiolar node and abdominal tergite III. Scapes and tibiae with dense depressed pubescence, without any standing hairs. Orifice without any radial hairs.

Colouration: Body black in colour. Head colour divided into two parts: orange anteriorly, up to ⅖ of the head and black–grey posteriorly, distinctly separated by a margin in frontal and lateral view. Mandibles and antenna red–brown. Coxa black–grey; trochanter orange; femur and tibia dark–brown; colour from basitarsus to the tarsal claw grades from dark–brown to dark orange.

 Comparative notes.

Within the Orthonotomyrmex species found in Southeast Asia, C. orthogonius sp. nov. most closely resembles C. siamensis from Thailand. Overall, C. orthogonius sp. nov. is larger than C. siamensis in both the minor (WL of C. orthogonius sp. nov. = 1.46–1.87; WL of C. siamensis = 1.29–1.42) and major (WL of C. orthogonius sp. nov. = 1.99–2.18; WL of C. siamensis = 1.72–1.75) worker subcastes. In the minor worker subcaste, C. orthogonius sp. nov. can be distinguished from C. siamensis by the following: in lateral view, metanotal groove moderately impressed instead of deeply impressed, the propodeum is relatively longer than C. siamensis and forms a continuous margin with the mesonotum, instead of elevated slightly above the mesonotum (Fig. 8), petiolar node relatively higher (PH of C. orthogonius sp. nov. = 0.34–0.47; PH of C. siamensis = 0.33–0.36) and weakly inclining anteriorly (Figs 4B, 6C, 6D, 7D); in dorsal view, the promesonotal suture outline is more sharply rounded instead of subtly rounded (Fig. 9). In comparison with minor workers of C. siamensis collected from Laos, C. orthogonius sp. nov. can be differentiated by the right–angled pronotal humeral corners, instead of acutely angled. In the major worker subcaste, C. orthogonius sp. nov. can be distinguished from C. siamensis by the following: with head in full–face view, head is wider than C. siamensis (HW of C. orthogonius sp. nov. = 1.58–1.70; HW of C. siamensis = 1.35–1.42), posterior margin nearly straight instead of weakly concave, antenna scape reaching posterodorsal corner of head (Figs 4A, 7C); in lateral view, propodeum is relatively longer, posterodorsal corners of propodeum right angled instead of narrowly rounded (Fig. 8), petiolar node weakly inclining anteriorly instead of strongly inclining anteriorly (Figs 4B, 7F); in dorsal view, anterior pronotal margin subtly convex to notably convex (Figs 4C, 7I). Only in Hainan Province, China have we recorded both species so far and specimens maintain the distinctness as discussed above; therefore, we believe that C. orthogonius sp. nov. is a distinct species from C. siamensis and not a result of allopatric speciation (Fig. 6).

10.3897/contrib.entomol.76.e189240.figure7 CA13B171-6CCD-5542-978A-20182DDE9F48

Camponotus siamensis non–type specimens from Bolikhamsai, Laos: minor worker (ANTWEB1011157) (A, D, G); median worker (ANTWEB1011158) (B, E, H); major worker (ANTWEB1011159) (C, F, I). A–C. Head in full–face view; D–F. Body in lateral view; G–I. Body in dorsal view.

https://binary.pensoft.net/fig/1748352 10.3897/contrib.entomol.76.e189240.figure8 65EA063E-3FF6-520D-99A8-D9E276AABE6E

Mesonotum and propodeum outline in lateral view (represented by red–dotted lines) of minor and major workers of Camponotus orthogonius sp. nov. (A. holotype minor worker, ANTWEB1010678; C. paratype major worker, ANTWEB1010676) and Camponotus siamensis (B. non–type minor worker, ANTWEB1011157; D. non–type major worker, ANTWEB1011159).

https://binary.pensoft.net/fig/1748353 10.3897/contrib.entomol.76.e189240.figure9 CF697A7D-6B4F-588B-958B-6C5AA14807E1

Mesosoma outline in dorsal view (represented by red–dotted lines) of minor workers of species in the selene–complex investigated in this study. A. Camponotus orthogonius sp. nov. (holotype, ANTWEB1010678); B. Camponotus siamensis (non–type, ANTWEB1011157); C. Camponotus obtusatus stat. nov. (non–type, ANTWEB1011370); D. Camponotus selene (syntype, CASENT0905415, photographer Ziv Lieberman, available from http://www.antweb.org).

https://binary.pensoft.net/fig/1748354

In China, C. orthogonius sp. nov. most closely resembles C. obtusatus stat. nov. and C. selene. Characters that distinguish the minor worker subcaste of C. orthogonius sp. nov. from the latter two species by the following: eyes are larger in C. orthogonius sp. nov. (EW of C. orthogonius sp. nov. = 0.33–0.41, EW of C. lasiselene syn. nov. = 0.24, EW of C. selene not provided); with head in full face view, posterolateral margins broadly convex, instead of bluntly angled in C. obtusatus stat. nov. (Figs 1A, 2A, 3A, 3B, 4A), antenna scape surpassing posterolateral corners of head by approximately ⅖ of its length instead of ⅓ of its length in C. obtusatus stat. nov. (Figs 1A, 2A, 3A, 3B, 4A); in lateral view, propodeal spines are absent, the apex of petiolar node rounded, instead of flat in C. obtusatus stat. nov. or angulate in C. selene and the body with sparse pilosity, instead of with dense pilosity (Figs 1B, 2B, 3C, 3D, 4B). In dorsal view, pronotum is narrower, the propodeum margin is narrow and straight instead a pair of forcipiform teeth (Fig. 9).

 Etymology.

The specific name refers to the right–angled propodeum in lateral view observed in both the minor and major workers. The epithet is the nominative singular masculine Latin adjective for “orthogonal”, meaning “at a right angle”.

 Distribution.

Camponotus orthogonius sp. nov. is recorded in Hong Kong where it has a wide local distribution, with specimens collected from Hong Kong Island, New Territories and Lantau Island. It is also found in Hainan Province and can also be suspected to be found in neighbouring provinces to Hong Kong in southern China, such as Guangdong and Guangxi Provinces. Records on iNaturalist of C. obtusatus stat. nov. in southeast China should be interpreted with caution and are, in some cases, misidentifications of C. orthogonius sp. nov.

 Ecology.

A nest of 148 individuals consisting of 73 minor workers, 13 major workers and 62 larvae, was collected on 3 April 2025 in multiple twigs from a dead tree in a young secondary forest near Tsing Tam Village, Hong Kong. The tree had collapsed due to ongoing slope maintenance, exposing the colony. However, no reproductives were observed or collected along with the nest. The presence of larvae and workers in multiple twigs suggests a potential polydomic structure of the colony, which would need to be confirmed in the future. Individual workers have been observed foraging on handrails in country parks during the day and have also been collected through vegetation beating and malaise trap. Individual foraging workers have also been found in small crevices between concrete tiles in a farmland in Hainan. Altogether, this suggests an arboreal nesting and foraging lifestyle in this species.

It is interesting to note that the major workers present partially phragmotic heads, similar to species in the Camponotus recitulatus–group (Ward et al. 2025) which resembles those observed in the genera Colobopsis and Gesomyrmex Mayr, 1868, also found in the region. Ward and Boudinot (2021) suggested that the similarity in the head morphology could be an example of convergent evolution, where the phragmotic heads of Colobopsis and some Camponotus species act as blockades to the nest entrance to prevent entry by intruders (Mayr 1861). However, this behaviour in C. orthogonius sp. nov. has not been observed directly in the field and can only serve as speculation at the moment.

 Animalia Hymenoptera Formicidae 5A130177-13C0-5927-9F53-F2278DCC6622 Camponotus siamensis Jaitrong & Jeenthong, 2022 Figs 6B , 6D , 6F , 7A–I Camponotus siamensis Jaitrong & Jeenthong, 2022: 34, figs 1A–F (s.w.) Thailand. Holotype minor worker. Primary type locality: Thailand: NE Thailand, Mukdahan Province, Chamcha–I District, Cheang Chang Niam Village, mixed deciduous forest (MDF), 8.vi.2007, WJT07–TH–1075 (W. Jaitrong). THNHM (images examined). 9 paratype minor workers, 3 paratype major workers. Secondary type locality: 7 paratype minor workers, 3 paratype major workers with same data as holotype; 2 paratype minor workers NE Thailand, Mukdahan Province, Chamcha–I District, Kheang [Cheang] Chang Niam Village, dry evergreen forest (DEF), 4.ix.2007 (W. Jaitrong). THNHM. Secondary type specimens: minor workers: THNHM–I–24795 to THNHM–I–24801, THNHM–I–24805, THNHM–I–24806; major workers: THNHM–I–24802 (images examined), THNHM–I–24803, THNHM–I–24804. Combination in Camponotus (Orthonotomyrmex): Jaitrong & Jeenthong, 2022: 34. Material examined.

China — Hainan Prov. • 1 minor worker; Diaoluoshan NNR; 27.v.1999; J R. Fellowes leg.; MBS013226; HKBM.

Laos — Bolikhamsai • 35 minor workers, 5 major workers; Ban Hat Khay; 18.427879°N, 103.151289°E; ± 20 m2; 196 m a.s.l.; 26.xi.2025; Hand coll.; B. Guénard leg.; Rub. Plant.; BG–PKK–02; IBBL • 1 minor worker; As previous; ANTWEB1011158; IBBL • 1 major worker; As previous; ANTWEB1011159; IBBL • 1 minor worker; As previous; ANTWEB1011177; ZRC • 1 minor worker; As previous; ANTWEB1011178; ZRC • 1 minor worker; As previous; ANTWEB1011179; IBBL • 1 major worker; As previous; ANTWEB1011180; ZRC • 1 minor worker; As previous; ANTWEB1011181; ZRC • 1 major worker; As previous; ANTWEB1011182; ZRC • 1 minor worker; As previous; ANTWEB1011183; IBBL • 1 minor worker; Ban Hat Khay; 18.4299°N, 103.15144°E; ± 50 m2; 192 m a.s.l.; 26.xi.2025; Hand coll.; B. Guénard leg.; Rubber Plantation; BG–PKK–03, ANTWEB1011184; IBBL • 1 minor worker; Ban Hat Khay; 18.42°N, 103.15°E; ± 1 km2; 176 m a.s.l.; 26.xi.2025; Hand coll.; B. Guénard leg.; Rubber Plantation; BG–PKK–13; ANTWEB1011157; IBBL.

 Distribution.

One minor worker was collected in Diaoluoshan Nature Reserve in Hainan Province, China in 1992, which presents a new record of the species in China and the northernmost record of this species so far.

Recently, more specimens were sampled in Bolikhamsai Province, Laos. The collection site was 248 km northwest of the where the type specimens were collected in Mukdahan Province, Thailand (Jaitrong and Jeenthong 2022). The discovery of this species also presents a new species record for the Lao People’s Democratic Republic.

 Ecology.

A nest of 112 individuals consisting of 41 minor workers, eight major workers and 73 larvae were collected from a rather large dead bamboo stem (diameter 10–15 cm). The bamboo patch was growing along a dry river stream and was nested within a rubber plantation. No reproductives were observed or collected along with the nest. Several larvae of Microdon (Diptera, Syrphidae) were also observed in the same bamboo stem.

 Comments.

Three median workers were discovered within the colony collected from Laos (Fig. 7B, E, H), which bear phragmotic heads with the shape and colour patterns similar to that of the major workers (Fig. 7C, F, I). The pronotum is also similar to that of the major workers, while the slightly elevated propodeum is similar to that observed in the minor workers.

Upon closer examination of the specimens from Laos, there appears to be some regional variation compared to the type specimens from Thailand: both the minor and major workers collected in Laos are observed to have more distinct triangular humeral corners of the pronotum in dorsal view; in the minor workers, in particular, the anterolateral margins of the pronotum are strongly concave in dorsal view rather than weakly concave in the type specimens from Thailand; the promesonotal suture in some minor workers were weakly rounded in dorsal view, which are similar to that observed in C. orthogonius sp. nov. The shape of the humeral corners of the pronotum seem to be variable between minor and major workers from both localities (Jaitrong, personal communication, February 2026). Other than these differences, all other characters observed in the Laos specimens correspond to the description of C. siamensis provided by Jaitrong and Jeenthong (2022).

 Key to minor workers in the <italic><tp:taxon-name><tp:taxon-name-part taxon-name-part-type="genus" reg="Camponotus">Camponotus</tp:taxon-name-part> <tp:taxon-name-part taxon-name-part-type="species" reg="selene">selene</tp:taxon-name-part></tp:taxon-name></italic>–complex
1 In dorsal view, propodeum bidentate, forming propodeal spines (Fig. 9C, D) 2
– In dorsal view, propodeum not bidentate (Fig. 9A, B) 4
2 In dorsal view, anterior pronotal margin convex, propodeum with fork–shaped teeth (Fig. 10E) Camponotus impressilabris Stitz, 1938
– In dorsal view, anterior pronotal margin straight, propodeum with hook–shaped teeth (Fig. 9C, D) 3
3 With head in full–face view, posterolateral margins broadly rounded. In dorsal view, anterior margin of pronotum with two concavities on each side (Figs 9D, 11A) Camponotus selene (Emery, 1889)
– With head in full–face view, posterolateral margins bluntly angled. In dorsal view, anterior margin of pronotum with one concavity on each side (Figs 1, 2, 3, 9C) Camponotus obtusatus (Emery, 1895), stat. nov.
4 In lateral view, mesosoma dorsum outline nearly continuous, only broken by metanotal groove, petiolar node relatively higher and weakly inclining anteriorly in lateral view (Figs 4B, 8A) Camponotus orthogonius sp. nov.
– In lateral view, mesosoma dorsum outline not continuous, with propodeum raised slightly above mesonotum, petiolar node relatively lower and strongly inclining anteriorly (Figs 5D, 8B) Camponotus siamensis Jaitrong & Jeenthong, 2022
Key to major workers in <italic><tp:taxon-name><tp:taxon-name-part taxon-name-part-type="genus" reg="Camponotus">Camponotus</tp:taxon-name-part> <tp:taxon-name-part taxon-name-part-type="species" reg="selene">selene</tp:taxon-name-part></tp:taxon-name></italic>–complex<sup><xref ref-type="fn" rid="FN1">1</xref></sup>
1 Head almost as long as wide. In lateral view, apex of petiolar node marginated. In dorsal view, posterior propodeum margin concave Camponotus obtusatus (Emery, 1895), stat. nov.
– Head longer than wide; in lateral view apex of petiolar node round. In dorsal view, posterior propodeum margin convex 2
2 In lateral view, frontal carina raised, side of head very finely punctate (Fig. 10B, D) Camponotus impressilabris Stitz, 1938
– In lateral view, frontal carina not raised, side of head coarsely punctate 3
3 With head in full–face view, scape just reaching posterolateral corners of head; in lateral view posterodorsal corner of propodeum right–angled, petiolar node weakly inclining anteriorly (Figs 5A, 5B, 8C) Camponotus orthogonius sp. nov.
– With head in full–face view, scape fails to reach posterolateral corners of head; in lateral view posterodorsal corner of propodeum narrowly rounded, petiolar node strongly inclining anteriorly (Figs 7C, 7F, 7I, 8D) Camponotus siamensis Jaitrong & Jeenthong, 2022
Discussion

The proposal of the C. selene–complex serves as a starting point to resolve the complicated taxonomy of the subgenus Orthonotomyrmex by uniting a group of morphologically congruent Southeast Asian species. Examination of Orthonotomyrmex specimens showed workers of different species exhibit distinct morphological disparities, particularly in the major workers (e.g. C. orthogonius sp. nov. versus C. sericeus). Considering the results from recent phylogenetic studies suggesting that members of the subgenus are scattered in at least two major clades with different biogeographic origins (Ward et al. 2025), the placement of both Oriental and Afrotropical species within the subgenus should be thoroughly re–assessed in the future to discern which members are true Orthonotomyrmex species.

10.3897/contrib.entomol.76.e189240.figure10 FE3C9EBD-6C79-56AE-AD9C-D63B68DF48F4

Camponotus impressilabris syntype workers: minor (FOCOL2273, photographer Christiana Klingenberg) (A–C); major (FOCOL2274, photographer Christiana Klingenberg) (D–F). A, D. Head in full–face view; B, E. Body in lateral view; C, F. Body in dorsal view. Images available from http://www.antweb.org.

https://binary.pensoft.net/fig/1748355 10.3897/contrib.entomol.76.e189240.figure11 0C6F0C97-7C73-5A89-AB92-8064A151E086

Camponotus selene syntype minor worker (CASENT0905415, photographer Ziv Lieberman). A. Head in full–face view; B. Body in lateral view; C. Body in dorsal view. Images available on from http://www.antweb.org.

https://binary.pensoft.net/fig/1748356 10.3897/contrib.entomol.76.e189240.figure12 FA320977-B7B2-53DD-A4D6-8605A93DB597

Geographical distribution of members of the selene–complex examined in this study.

https://binary.pensoft.net/fig/1748357

Species checklist of members of the selene–complex in China and Southeast Asia. + = Presence; – = No record; NR = New record from this study; P = Potential presence as discussed.

Species Country/Province/Region
Fujian Guangdong Guangxi Hainan Hong Kong Hunan Laos Malaysia Myanmar Thailand Vietnam Xizang Yunnan
Camponotus impressilabris Stitz, 1938 – – – – – – – + – – – – –
Camponotus obtusatus (Emery, 1895), stat. nov. NR + + – – + – – + + + + +
Camponotus orthogonius sp. nov. – P P NR NR – – – – – – – –
Camponotus selene (Emery, 1889) – – + – – + – – + – – – +
Camponotus siamensis Jaitrong & Jeenthong, 2022 – – – NR – – NR – – + – – –
Total 1 2 3 2 1 2 1 1 2 2 1 1 2

The discovery of the new species C. orthogonius sp. nov. from southeast China and the range expansion of C. obtusatus stat. nov. and C. siamensis in Southeast Asia confirm the potential for new discoveries in the region as illustrated in recent years for arboreal ant species (Luo and Guénard 2017; Wong and Guénard 2021; Chen and Chen 2022; Jaitrong and Jeenthong 2022; Hamer et al. 2023; Qian and Xu 2024; Chen et al. 2025; Phosrithong et al. 2025), as well as for many other new species and new record species from Hong Kong (e.g. Tang et al. (2019); Hamer et al. (2025)). The exploration of the arboreal ant communities in Southeast Asia deserves further effort to collect this less accessible fauna, while careful examination should be performed to identify potential new species.

 Acknowledgements

The authors would like to express gratitude to Mr. Wu Yat Hong (Y. H. Wu) and Mr. Benjamin Walker Heath (B. W. Heath), two undergraduate volunteers at the Insect Biodiversity and Biogeography Laboratory, who are responsible for collecting the C. orthogonius sp. nov. colony which comprises of the type specimens used in this study as well as other materials for examination. The authors would also like to thank Mr. André Ibáñez and Dr. Junaid Ali Siddiqui for providing C. orthogonius sp. nov. specimens from Hainan, Mr. Liu Xuan for the collection of C. obtusatus stat. nov. from Fujian and Dr. John R. Fellowes for the collection of C. siamensis from Hainan and C. obtusatus stat. nov. from Guangdong and Guangxi. The authors would also like to thank Professor Hong–Bin Wang and Dr. Mei Wang (Organism Specimen Collection, Institute of Forest Ecological Environment and Nature Conservation, Chinese Academy of Forestry, Beijing) for providing the holotype worker of C. lasiselene syn. nov., Professor Zheng–Hui Xu, Dr. Zhi–Lin Chen and Dr. Xin–Min Zhang for imaging the holotype specimen and Professor Zheng–Hui Xu for providing the images of the holotype specimen for examination. We also warmly thank Dr. Jaitrong Weeyawat for providing further collection information on the type series of C. siamensis and insights into the specimens from Laos and Mr. Bertrand Laville for his assistance in Laos. Finally, we would like to thank Professor Zheng–Hui Xu, Dr. Brendan Boudinot, Dr. Jaitrong Weeyawat and an anonymous reviewer for their invaluable comments for improving the manuscript. This work was supported by grants from the Research Grant Council of the Hong Kong Government, 2023/2024 General Research Fund project #17103223 and project #17121922, as well by a grant from the Lantau Conservation Fund RE–2021–14.

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The authors have declared that no competing interests exist.

 Ethical statement

No ethical statement was reported.

 Artificial Intelligence (AI) use

The authors accept full responsibility for the content of the manuscript, including the disclosure of any use of AI.

No AI tools were used in the preparation of this manuscript.

 Funding

Research Grant Council of the Hong Kong Government, 2023/2024 General Research Fund project #17103223 and project #17121922 2. Lantau Conservation Fund RE-2021-14

 Author contributions

Conceptualization: Marco Chan, Matthew T. Hamer, Benoit Guénard. Data curation: Marco Chan. Formal analysis: Marco Chan, Matthew T. Hamer. Funding acquisition: Benoit Guénard. Investigation: Marco Chan, Matthew T. Hamer. Methodology: Marco Chan, Matthew T. Hamer. Supervision: Benoit Guénard. Validation: Matthew T. Hamer, Benoit Guénard. Visualization: Marco Chan. Writing – original draft: Marco Chan, Matthew T. Hamer. Writing – review & editing: Marco Chan, Matthew T. Hamer, Benoit Guénard.

 Author ORCIDs

M. Chan https://orcid.org/0009-0001-4459-3966

M.T. Hamer https://orcid.org/0000-0001-6728-9046

B. Guénard https://orcid.org/0000-0002-7144-1175

 Data availability

All of the data that support the findings of this study are available in the main text or Supplementary Information.

Camponotus selene is excluded from the key because the major worker is not known.

 Supplementary materials 10.3897/contrib.entomol.76.e189240.suppl1 438839FB-3C3D-5B2C-96E3-2DF4140E44B6

Measurements of Camponotus orthogonius sp. nov.

xlsx

Morphological measurements of type and non-type specimens of the newly described Camponotus orthogonius sp. nov.

 https://binary.pensoft.net/file/1748358 This dataset is made available under the Open Database License (http://opendatacommons.org/licenses/odbl/1.0). The Open Database License (ODbL) is a license agreement intended to allow users to freely share, modify, and use this Dataset while maintaining this same freedom for others, provided that the original source and author(s) are credited. Author: Marco Chan