Belongs within: Staphylinidae.
Contains: Euconnini, Cyrtoscydmini.
The Scydmaeninae, ant-like stone beetles, are a group of minute beetles found in habitats such as leaf litter or moss, or in association with ants or termites (O’Keefe 2001). Though long treated as their own family, more recent phylogenetic studies have established that they are derived within the Staphylinidae and they are now treated as a subfamily within that larger grouping. Where their natural history is known, scydmaenids are specialist predators of oribatid mites.
The Cretaceous Hapsomela has been assigned to its own supertribe on the basis of an apparent ‘patella’ in the fore legs, though the exact nature of this structure is debated (Grebennikov & Newton 2009).
Characters (from O’Keefe 2001, as Scydmaenidae): Body elongate, slender to ovoid; slightly to very convex, 0.6–2.7 mm long; often distinctly constricted between head and pronotum and between pronotum and elytra, usually light to dark brown, sometimes black in color; often densely pubescent on head, pronotum, and elytra, pubescence usually long. Head short and broad to ovoid; deflexed; usually distinctly constricted between vertex and occiput; occiput formed into a “neck”; clypeofrontal region moderate in length, slightly narrowed anteriorly. Eyes anterior, median, or posterior; moderate in size or absent. Antennae inserted anterior to eyes, antennal insertions adjacent to widely separated; antennae composed of scape, pedicel and nine flagellomeres; antennal club composed of distal three to five antennomeres, from indistinct to distinct in form. Mandibles usually planar, subtriangular with large basal area, narrowed to acute incisor, subapical teeth usually absent. Maxillary palpus composed of four palpomeres; palpomere III large, clavate; palpomere IV variable, distinctly smaller than III; apices of lacinea and galea densely covered with long setae. Labial palpus composed of three palpomeres; mentum large. Thorax with pronotum distinctly wider than head, usually with fovea or transverse furrow along posterior margin. Scutellum small, visible, occasionally hidden. Elytra ovoid, convex to rectangular, flat; humeri varied in form with 0-2 basal foveae in broad basal impression; elytral apices usually entire, occasionally truncate or fused. Hind wings, if present, well-developed. Legs relatively short to moderate in length; procoxae projecting beyond prosternum, procoxal cavities open; mesocoxal cavities closed; trochanters relatively large and sublinear or rounded triangular; femora strongly clavate in distal half; protibiae and mesotibiae usually with dense patches of setae at distal end. Prosternum varied from subquadrate to very narrow before conical, contiguous procoxae, pubescence varied. Mesosternum usually raised, sometimes densely setose, bearing mid-ventral carina separating otherwise contiguous mesocoxae. Metasternum long, broad, occasionally carinate or medially excavate; metacoxae round to transverse, conical, widely separate to contiguous. Abdomen with six visible sternites. Male genitalia with median lobe bulbous, large, to elongate, to reduced, lightly sclerotised, distinctly curved, parameres long, slender, articulated on dorsal surface of aedeagus, occasionally absent. Ovipositor composed of paired, fused or unfused dorsolateral paraprocts, triangular dorsal proctiger, paired elongate ventral valvifers, paired elongate gonocoxae; gonostyli absent; spermatheca present, variable in shape from elongate, slender to spherical, accessory gland sometimes present.
<==Scydmaeninae [Anisosphaeridae, Scydmaenidae, Scydmaenides]
|--Hapsomela [Hapsomelinae, Hapsomelitae]GN09
`--ScydmaeinitaeGN09
| i. s.: PlaumannioliniGN09
| Chevrolatia Jacquelin du Val 1850O01 [ChevrolatiiniGN09]
| |--C. amoena LeConte 1866B14
| `--C. occidentalisB14
| Leptoscydmus Casey 1897O01 [LeptoscydminiGN09]
| `--L. caseyiO01
|--+--Cephennodes Reitter 1884LC20, GN09
| | `--C. clavatusLC20
| `--EutheiiniO01
| |--Eutheia Stephens 1830 [=Euthia Agassiz 1847; incl. Euthiopsis Müller 1925]O01
| |--Euthiconus Reitter 1881 [incl. Ascydmus Casey 1897, Euthiodes Brendel 1893]O01
| | `--E. lataO01
| `--Veraphis Casey 1987GN09
| `--V. cristataO01
`--+--Mastigitae [Mastiginae]GN09
| |--LeptomastaciniGN09
| |--MastiginiMF15
| | |--MastigusP92 [MastiginiGN09]
| | | |--M. palpalisL02
| | | `--M. spinicornis [=Ptinus spinicornis]L02
| | `--Palaeostigus Newton 1982MF15, GN09
| | `--P. bifoveolatus (Boheman 1851)GN09
| `--ClidiciniGN09
| |--ClidicusLC20
| `--Papusus Casey 1897O01
| `--P. macerO01
`--+--NeuraphesLC20
`--+--ScydmaeniniMW01
| |--PalaeoscydmaenusLB91
| |--Ceramphis Casey 1897O01
| | `--C. deformataO01
| |--AdrastiaMF15
| `--Scydmaenus Latreille 1802LC20, GN09 (see below for synonymy)
| |--S. angustatus Lucas 1846E12
| |--S. godarti [=Mastigus (Scydmenus) godarti]G20
| |--S. hellwigii [=Pselaphus hellwigii]L02
| |--S. motschulskiiO01
| |--S. myrmecophilusLB91
| |--S. nanus Lucas 1846E12
| |--S. schaumii Lucas 1846E12
| `--S. tarsatusRD77
`--+--CephenniiniGN09
| |--CoatesiaLB91
| |--NeseuthiaLB91
| |--Chelonoidum Strand 1935 [=Chelonoides Croissandeau 1894]O01
| | `--C. corporosumO01
| `--Cephennium Müller & Kunze 1822LC20, O01
| |--C. anophthalmicumO01
| |--C. gallicumLC20
| `--C. thoracicum (Müller & Kunze 1822)B14
`--+--EuconniniLC20
`--CyrtoscydminiLC20
Scydmaeninae incertae sedis:
PhagonophanaB70
Heterognathus myrmecophilusB70
Syndicus [Syndicini]LB91
PalaeoleptochromusGN09
CryptodiodonP92
ElectroscydmaenusP92
HetereuthiaP92
HeuretusP92
PalaeomastigusP92
PalaeothiaP92
SemnodiocerusP92
ScydmaenoidesP92
MegalederusP92
Scydmaenus Latreille 1802LC20, GN09 [incl. Acholerops Casey 1897O01, Eumicrus LaPorte 1840O01, Microstemma Motschulsky 1858O01]
*Type species of generic name indicated
References
[B14] Bouchard, P. (ed.) 2014. The Book of Beetles: A lifesize guide to six hundred of nature’s gems. Ivy Press: Lewes (United Kingdom).
[B70] Britton, E. B. 1970. Coleoptera (beetles). In: CSIRO. The Insects of Australia: A textbook for students and research workers pp. 495–621. Melbourne University Press.
[E12] Evenhuis, N. L. 2012. Publication and dating of the Exploration Scientifique de l’Algérie: Histoire Naturelle des Animaux Articulés (1846–1849) by Pierre Hippolyte Lucas. Zootaxa 3448: 1–61.
[G20] Goldfuss, G. A. 1820. Handbuch der Naturgeschichte vol. 3. Handbuch der Zoologie pt 1. Johann Leonhard Schrag: Nürnberg.
[GN09] Grebennikov, V. V., & A. F. Newton. 2009. Good-bye Scydmaenidae, or why the ant-like stone beetles should become megadiverse Staphylinidae sensu latissimo (Coleoptera). European Journal of Entomology 106: 275–301.
[L02] Latreille, P. A. 1802. Histoire Naturelle, générale et particulière des crustacés et des insectes vol. 3. Familles naturelles des genres. F. Dufart: Paris.
[LB91] Lawrence, J. F., & E. B. Britton. 1991. Coleoptera (beetles). In: CSIRO. The Insects of Australia: A textbook for students and research workers 2nd ed. vol. 2 pp. 543–683. Melbourne University Press: Carlton (Victoria).
[LC20] Lü, L., C.-Y. Cai, X. Zhang, A. F. Newton, M. K. Thayer & H.-Z. Zhou. 2020. Linking evolutionary mode to palaeoclimate change reveals rapid radiations of staphylinoid beetles in low-energy conditions. Current Zoology 66 (4): 435–444.
[MF15] McKenna, D. D., B. D. Farrell, M. S. Caterino, C. W. Farnum, D. C. Hawks, D. R. Maddison, A. E. Seago, A. E. Z. Short, A. F. Newton & M. K. Thayer. 2015. Phylogeny and evolution of Staphyliniformia and Scarabaeiformia: forest litter as a stepping stone for diversification of nonphytophagous beetles. Systematic Entomology 40: 35–60.
[MW01] Molleman, F., & D. E. Walter. 2001. Niche segregation and can-openers: scydmaenid beetles as predators of armoured mites in Australia. In: Halliday, R. B., D. E. Walter, H. C. Proctor, R. A. Norton & M. J. Colloff (eds) Acarology: Proceedings of the 10th International Congress pp. 283–288 Publishing: Melbourne.
[O01] O’Keefe, S. T. 2001. Scydmaenidae Leach, 1915. In: Arnett, R. H., Jr & M. C. Thomas (eds) American Beetles vol. 1. Archostemata, Myxophaga, Adephaga, Polyphaga: Staphyliniformia pp. 259–267. CRC Press: Boca Raton.
[P92] Poinar, G. O., Jr. 1992. Life in Amber. Stanford University Press: Stanford.
[RD77] Richards, O. W., & R. G. Davies. 1977. Imms’ General Textbook of Entomology 10th ed. vol. 2. Classification and Biology. Chapman and Hall: London.