Ground beetles in the genus Pterostichus, subgenus Euferonia, are common woodland beetles in the eastern U.S. Almost all have reduced wings, so are unable to fly.
I’ve collected a number of specimens that fit into this species pair, but have struggled with separating them with existing keys. Lindroth noted that “the infraspecific variation of external characters is considerable” and has resulted in many unnecessary names, especially by Casey.
The characters that separate P. stygicus from P. coracinus are the presence of a “tubercle” in the basal fovea of the pronotum and the elytra usually being somewhat iridescent. The iridescence isn’t hard to see, but the “tubercle” is very subjective. It appears to be referring to a low ridge or convexity within the fovae, hardly tuberculate in my opinion, and quite variable. Fortunately, I recently collected a pair of males and decided to consult Lindroth, who illustrates the genitalia of the species. The shape of the penis is very distinct between the two species: symmetrical in P. stygicus and asymmetical in P. coracinus. This led to the reevaluation my previously collected specimens, which turned out to be all P. stygicus.
Now I just need to find P. coracinus!
It’s that time again, when an excess of specimens requires the splitting up of a specimen box. Not that this is a bad thing; actually it’s great, as long as you have an extra box sitting around.
I’ve been putting away some identified specimens, but I just couldn’t find any room for some new Latridiidae. So its time to split it up, which I’ve been putting off for awhile. Actually, I probably have four or five boxes that need splitting now that I think about it….
Here is the before picture. Yeah, sloppy I know. Kudos if you can guess all 12 families I have stuffed in this box.
A recent post on BugGuide brought to my attention to a group of fungi known as Laboulbeniales that infect insects. I knew I had seen these before, but I had never really paid them much attention. Sorting through some Carabidae I had collected this summer, I noticed one of the strange growths on the elytron of a Clivina americana. After posting an image of this beetle to BugGuide, I continued sorting the sample. To my surprise, I found the fungal hyphae on a large number of specimens. Once I had seen the first, they became fairly easy to spot (despite all the moth scales floating around in the alcohol).
I contacted the author of the Laboulbeniales post, Danny Haelewaters, now a doctoral student at the Farlow Herbarium, Harvard University. He is studying Laboulbeniales fungi, so I’ll be sending the specimens to him for his research.
The Carabidae that appeared infected included Clivina americana, Perigona nigriceps, Elaphropus xanthopus, Acupalpus partiarius, Acupalpus indistinctus, Bradycellus rupestris, Stenolophus lecontei, and Stenolophus ochropezus. There were also infected Homaeotarsus cf. bicolor (Staphylinidae) and Melanophthalma sp. (Latridiidae).
Below are images of some infected beetles (Homaeotarsus, Melanophthalma, Elaphropus xanthopus, and Stenolophus ochropezus):
I was fortunate this summer to take a short series of Neobisnius specimens while black-lighting in Kentucky. Some species are quite colorful and have a very similar color pattern to the toxic Paederus, and may well be mimics. Luckily there is a thorough monograph of this genus by JH Frank (1980). Males are fairly easy to key out using external characters, although examination of the aedeagus is probably advisable. The tricky part is that males and females aren’t terribly different externally. The front tarsi are somewhat dilated in both sexes! The keys do not work for females, and there are reproductions of Frank’s key that fail to mention it is based on males (*cough*Downie&Arnett*cough*).
I recommend a quick dissection before mounting this group to determine sex. If a male, the aedeagus is usually easily evertable and left attached to the beetle, or it can be glued to a point below the specimen.There are five species of Neobisnius in the midwest that have this Paederus-like color pattern (referred to as “parti-colored” by Horn): N. jocosus, N. jucundus, N. occidentoides, N. paederoides, and N. terminalis. An additional similarly colored species, N. ludicrus, occurs in the east, but appears restricted to the coastal states of the Southeast. A quick key to males of the 5 ‘parti-colored’ species is as follows, but genitalia should always be checked when possible:
- Head with a fovea on head between antennae. 2
Head without such a fovea. 3 Eyes large, almost 1/2 length of head … N. occidentoides Frank
Eyes smaller, only about 1/3 length of head … N. jucundus (Horn) Pale apical elytral band about 1/4 length of elytra … N. terminalis (LeConte)
Pale apical elytral band very narrow. 4 Less than 5 mm, sides of head rounded; base of abdominal tergum 7 reddish … N. paederoides (LeConte)
Larger than 5 mm, head more parallel-sided; abdominal tergum 7 entirely black … N. jocosus Horn
In the series mentioned earlier, out of 13 specimens, 6 were female and 7 were male. Of the males, 2 were Neobisnius paederoides (LeConte) and 5 were Neobisnius occidentoides Frank. The females remain unidentified to species.
Frank, J.H. 1981. A revision of the new world species of the genus Neobisnius Ganglbauer (Coleoptera: Staphylinidae: Staphylininae). Occ. Papers of the Florida State Collection of Arthropods, 1: vi + 60 pp.
One problem I regularly see with rove beetles, particularly with some of the smaller groups, is that the abdomen shrinks as it dries, telescoping inward and potentially obscuring important characters. A fairly easy way to avoid this is by soaking the beetle(s) in acetone overnight, though I think 3 or 4 hours would be sufficient. The beetles are removed the next day and placed under a heat source (I use an incandescent light bulb) for a few minutes. The acetone tends to harden tissues and as it rapidly evaporates in the heat, the soft tissues remain rigid. Thus you get a well-preserved, un-shrunken specimen, although results do vary somewhat. One downside to this is specimens that have become distended from preservation in fluids will retain this appearance, but I don’t think this is a huge issue.
I use a similar technique for small flies and wasps.
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.