Belongs within: Harpalinae.
Contains: Scopodes.
The Odacanthini are a cosmopolitan group of ground beetles characterised by a short first antennal segment, not forming a distinct scape, together with the head being posteriorly narrowed to a ‘neck’ and the prothorax being subcylindrical. Many Odacanthini produce formic acid for defense but some genera such as Pentagonica and Scopodes produce saturated acids instead. Such genera have historically been treated as a distinct tribe Pentagonicini but are united with the Odacanthini by phylogenetic analysis.
Two become one
Published 20 October 2025
Historically, the classification of the Carabidae, the ground beetles, has been a chaotic affair. Almost no two authors used the same system, with much disagreement about which clusters of taxa should be recognised as subfamilies, tribes, what have you. Such is the case with the subjects of today’s post, the Odacanthini.
As recognised by Liebherr (1990), the Odacanthini are a globally distributed group with their highest diversity in the tropics. Previous authors had divided its members between two distinct tribes, the Pentagonicini and Odacanthini, that were distinctly different in appearance. ‘Odacanthini’ had a slender, cylindrical pronotum whereas that of ‘Pentagonicini’ was broader with angular sides. Nevertheless, Liebherr identified shared features of both male and female reproductive structures that united the two ‘tribes’. Conversely, pronotum shape appeared prone to convergence within the clade. As a result, Liebherr proposed combining the two tribes into one. This proposal was not universally accepted. In particular, Ball & Bousquet (2001) maintained separate tribes on the basis of differences in defensive chemistry: ‘odacanthines’ produced formic acid, supposedly a derived character within the broader subfamily Harpalinae, whereas ‘pentagonicines’ produced saturated acids, a more plesiomorphic character. However, Liebherr’s arrangement was supported by molecular analysis of harpalines (Ober & Maddison 2008). This analysis also confirmed ‘pentagonicine’ non-monophyly. The question of what this means for the evolution of defensive chemicals seems to still be up in the air, though I will note that I haven’t found exactly which genera of Odacanthini have been investigated chemical-wise.
More recently, Liebherr (2016) divided the Odacanthini between four subtribes. The basalmost of these included a single genus, the New Zealand Actenonyx, that retained plesiomorphic reproductive structures. The next to diverge, the Homethina, includes six genera with a Gondwanan distribution, found in the Neotropics, Indo-Australia, and New Caledonia. These genera were united by a distinctive feature of the mouthparts, a single-segmented maxillary galea that sat appressed to the outside of the lacinia. The remaining genera of Odacanthini were divided between two cosmopolitan subtribes, the Pentagonicina and Odacanthina, that each corresponded to the bulk of the historical tribes. The slender habitus of most Odacanthina, which is paralleled in a number of other harpaline tribes, may be an adaptation for ant-mimicry.
Systematics of Odacanthini
<==Odacanthini [Casnoniae, Colliurini, Lasiocerini, Pentagonicinae, Pentagonicini, Pentagonicitae, Scopodini] |--Pentagonica Schmidt-Goebel 1846OM08, LM87 (see below for synonymy) | |--*P. ruficollis Schmidt-Goebel 1846 [incl. P. dichroa Sloane 1903]LM87 | |--P. atkinsoni Fauvel 1882LM87 | |--P. blanda Andrewes 1929LM87 | |--P. conradtiB55 | |--P. elegansB55 | |--P. erichsoni Schmidt-Goebel 1846LM87 | |--P. felix Bell 1987BB01 | |--P. flavipesBB01 | |--P. olivacea Chaudoir 1877LM87 | |--P. pallipes (Nietner 1856) [=Elliotia pallipes]LM87 | |--‘Rhombodera’ picea Fleutiaux & Sallé 1890FS90 | |--P. picticornis Bates 1883BB01 | |--P. roedingeriOM08 | `--P. vittipennis Chaudoir 1877 [incl. *Wakefieldia vittata Broun 1880]LM87 `--+--+--Celaenephes Schmidt-Goebel 1846OM08, LM87 [incl. Taromorpha Blackburn 1894LM87] | | |--*C. parallelus Schmidt-Goebel 1846LM87 | | `--C. linearis (Walker 1858) [=Leistus linearis; incl. *Taromorpha alternata Blackburn 1894]LM87 | `--+--LasioceraOM08 | `--+--Stenidia rugucollisOM08 | `--+--Clarencia Sloane 1917OM08, LM87 | | |--*C. aliena (Pascoe 1860) (see below for synonymy)LM87 | | `--C. quadridens Darlington 1968LM87 | `--Dicraspeda Chaudoir 1862OM08, B12 | |--*D. brunnea Chaudoir 1862 [incl. Eudalia sublaevis Macleay 1888]LM87 | |--D. brunneipennis (Sloane 1917) [=Eudalia brunneipennis]LM87 | |--D. dubia (Gestro 1879) [=Odacantha dubia]LM87 | |--D. nitida (Sloane 1917) [=Eudalia nitida]LM87 | `--D. obscura (Castelnau 1867) [=Casnonia obscura]LM87 `--+--+--Actenonyx bembidiodesOM08 | `--ScopodesOM08 `--+--Casnoidea Castelnau 1834LM87 | |--*C. cyanocephala (Fabricius 1798) [=Cicindela cyanocephala]LM87 | |--C. puncticollis (Sloane 1923) [=Ophionea puncticollis]LM87 | `--C. thouzeti (Castelnau 1867) [=Ophionea thouzeti]LM87 `--Colliuris De Geer 1774OM08, BB01 [=Casnonia Latreille 1822BB01] | i. s.: ‘Casnonia’ flavicauda Bates 1873B89 | C. longicollis [=Collyris longicollis]L02 | C. par Darlington 1968LM87 |--*C. (Colliuris) surinamensis (Linnaeus 1766) [=Attelabus surinamensis, *Casnonia surinamensis]LM87 |--C. (Calocolliuris Liebke 1938) [=Calocollius (l. c.)]BB01 | `--C. (C.) ludoviciana (Sallé 1849)BB01 `--C. (Cosnania Dejean 1821) [incl. Odacanthella Liebke 1930]BB01 |--C. (C.) lengi (Schaeffer 1910)BB01 |--C. (C.) lioptera (Bates 1891)BB01 `--C. (C.) pensylvanica (Linnaeus 1767)BB01 Odacanthini incertae sedis: Odacantha melanura [=Brachinus (Odacantha) melanurus]G20 Porocara Sloane 1917B12 `--*P. punctata Sloane 1917LM87 Eudalia Castelnau 1867B12 |--*E. latipennis (Macleay 1864) [=Odacantha latipennis; incl. E. waterhousii Castelnau 1867]LM87 |--E. castelnaui Sloane 1910LM87 |--E. froggatti Macleay 1888LM87 |--E. macleayi Bates 1871LM87 |--E. nigra Sloane 1900LM87 `--E. obliquiceps Sloane 1917LM87 Parascopodes Darlington 1968LM87 `--*P. cyaneus (Sloane 1907) [=Scopodes cyaneus]LM87 Aeolodermus Andrewes 1929BB01 `--A. emarginatus (Chaudoir 1872) [=Homothes (l. c. for Homethes) emarginatus]LM87 Homethes Newman 1842BB01 [=Homothes (l. c.)LM87] |--*H. elegans Newman 1842 [incl. H. micans Germar 1848]LM87 |--H. angulatus Blackburn 1892LM87 |--H. gracilis Blackburn 1892LM87 |--H. guttifer Germar 1848LM87 |--H. marginipennis Macleay 1871LM87 |--H. niger Sloane 1920LM87 |--H. rotundatus Blackburn 1892LM87 |--H. sericeus (Erichson 1842) (see below for synonymy)LM87 `--H. velutinus Macleay 1871LM87
*Clarencia aliena (Pascoe 1860) [=Casnonia aliena; incl. Ca. angusticollis Macleay 1888, Ca. australis Chaudoir 1862, Ca. clarensii Castelnau 1867]LM87
Homethes sericeus (Erichson 1842) [=Euleptus sericeus; incl. H. parvicollis Blackburn 1892, H. vicinus Sloane 1898, Homothes (l. c.) vicinus]LM87
Pentagonica Schmidt-Goebel 1846OM08, LM87 [incl. Didetus LeConte 1853BB01, Rhombodera Reiche 1842 (preoc.)BB01, Wakefieldia Broun 1880LM87]
*Type species of generic name indicated
References
[B12] Baehr, M. 2012. A new species of the genus Pheropsophus (Coleoptera: Carabidae: Brachininae) from northern Australia. Records of the Western Australian Museum 27 (1): 62–67.
[BB01] Ball, G. E., & Y. Bousquet. 2001. Carabidae Latreille, 1810. In: Arnett, R. H., Jr & M. C. Thomas (eds) American Beetles vol. 1. Archostemata, Myxophaga, Adephaga, Polyphaga: Staphyliniformia pp. 32–132. CRC Press: Boca Raton.
[B55] Basilewsky, P. 1955. Carabidae (Coleoptera) de l’Angola (première partie). Diamang Publicações Culturais 27: 91–137.
[B89] Bates, H.-W. 1889. Contributions a la faune Indo-Chinoise. 3e mémoire. Carabidae. Annales de la Société Entomologique de France, 6e série 9: 261–286.
[FS90] Fleutiaux, E., & A. Sallé. 1890. Liste des coléoptères de la Guadeloupe et descriptions d’espèces nouvelles. Annales de la Société Entomologique de France, 6e série 9: 351–484.
[G20] Goldfuss, G. A. 1820. Handbuch der Naturgeschichte vol. 3. Handbuch der Zoologie pt 1. Johann Leonhard Schrag: Nürnberg.
[L02] Latreille, P. A. 1802. Histoire Naturelle, générale et particulière des crustacés et des insectes vol. 3. Familles naturelles des genres. F. Dufart: Paris.
[LM87] Lawrence, J. F., B. P. Moore, J. E. Pyke & T. A. Weir. 1987. Zoological Catalogue of Australia vol. 4. Coleoptera: Archostemata, Myxophaga and Adephaga. Australian Government Publishing Service: Canberra.
Liebherr, J. K. 1990. A new tribal placement for the Australasian genera Homethes and Aeolodermus (Coleoptera: Carabidae: Odacanthini). Pan-Pacific Entomologist 66 (4): 312–321.
Liebherr, J. K. 2016. Cyphocoleus Chaudoir (Coleoptera, Carabidae, Odacanthini): descriptive taxonomy, phylogenetic relationships, and the Cenozoic history of New Caledonia. Deutsche Entomologische Zeitschrift 63 (2): 211–270.
[OM08] Ober, K. A., & D. R. Maddison. 2008. Phylogenetic relationships of tribes within Harpalinae (Coleoptera: Carabidae) as inferred from 28S ribosomal DNA and the wingless gene. Journal of Insect Science 8: 63.