This afternoon, after having success identifying a specimen I collected earlier this year, I decided to take some time and identify my small collection of Scydmaenids, or “ant-like stone beetles”. These tiny beetles have recently lost family status and been sunk into a subfamily of the huge Staphylinidae family.
While not impressive in their size, these tiny beetles (as small as 1/2 mm to no larger than 3 mm) are still visually impressive under the microscope. But their small size requires high magnification to see some of the smaller details, such as the small foveae that a number of genera possess on their pronotums or elytra. Most genera have a shiny brownish to black “ant-like” habitus, some thickly beset with setae, especially in some of the Euconnus. However, the Cephenniini have a more Leiodid-like appearance.
I feared a difficult task was at hand, but identification of my 18 specimens to genus was fairly straightforward using the key in American Beetles Volume 1 (pg 259), which illustrates the key characters very well. (Unfortunately, species-level identifications for most of our fauna is nearly impossible, as the last major treatment was by Thomas Casey in 1897. Recent work by Sean O’Keefe [Morehead State University] is improving our knowledge of this neglected group.)
I only had representatives of 4 of the 12 genera I might expect in the Midwest. Here is a breakdown of what I found:
- 1 Chevrolatia amoena LeConte
- 2 Stenichnus
- 7 Scydmaenus
- 8 Euconnus, 4 in the subgenus Napochus and 4 in the subgenus Scopophus
I also have a specimen of Microscydmus, but it must still be in a vial of alcohol as I can’t find a mounted specimen.
Collecting methods used were:
- sifting debris that had accumulated under the loose bark of a standing dead tree, which yielded both of my Stenichnus and 6 of my Scydmaenus specimens (sample taken in early March which produced a large number of small beetles who were presumably overwintering in this microhabitat)
- berlese extraction of a blackened ‘pipe fungus’ yielded one Scydmaenus
- berlese extraction of material from a rotten log yielded one Euconnus (Scopophus)
- panel traps yielded one Chevrolatia and one Euconnus from each of the above subgenera
- Lindgren funnel traps yielded 3 specimens of Euconnus (Napochus)
- UV light trap yielded one specimen of Euconnus (Scopophus)
The only identification I am somewhat unsure about is a specimen tentatively ID’d as Euconnus (Scopophus) sp. taken via panel trap in Hays Co., Texas. It differs from the my other specimens in having rings of broad, white, scale-like setae circling the apical end of the four antennal segments making up the the club.
Visit BugGuide and browse the Scydmaeninae: link
- O’Keefe, S.T. 2001. American Beetles, Volume 1, Chapter 20: Scydmaenidae. pg.259-267.
- O’Keefe, S.T. 1997. Revision of the genus Chevrolatia Jacquelin du Val (Coleoptera: Scydmaenidae) for North America. Trans. Amer. Ent. Soc., 123: 163-185.