As I slowly scanned my flashlight through the darkness across the mixed-grass prairie in the Glass Mountains of northwestern Oklahoma last July, there was one thing that I hoped not to see (prairie rattlesnake, unless from afar) and one thing that I hoped more than anything to see (Great Plains giant tiger beetle, Amblycheila cylindriformis). Fortunately, I encountered none of the former and found several of the latter. It took awhile before I saw the first one, but in the meantime I saw all too abundantly the clown beetle, Eleodes suturalis. A member of the family Tenebrionidae, this species is one of the most conspicuous components of the Great Plains beetle fauna. Adults are commonly encountered walking about the grasslands or crossing roads, especially after summer rains. I recall my first encounter with this species when I made my first insect collecting trip to the Great Plains in 1986, marveling as I literally watched hundreds of individuals crossing a remote highway in southwestern Kansas. Now, they were just an annoyance – close enough in size and appearance to the object of my search that I had to pause and look at each one I encountered to verify its identity.¹
¹ In fact, a mimetic association has been suggested for Amblycheila cylindriformis and Eleodes suturalis due to their similarity in size, shape and coloration (black with a reddish-brown sutural stripe) (Wrigley 2008). This may be true, as Eleodes suturalis is an abundant species capable of defending itself with noxious sprays that contain benzoquinone and other hydrocarbons, while Amblycheila cylindriformis is a much rarer species (as mimics tend to be) that lacks defensive compounds.
After finding a few of the Amblycheila, I encountered this particular individual clinging to a root sticking out of the side of a wash. My closer look caused it to immediately assume its characteristic defensive headstand pose (from which the name ‘clown beetle’ comes), so I decided to take a few photographs (not an easy task at night). The photos have been sitting on my hard drive since, but in examining them more closely, I realized that this particular beetle is not E. suturalis. Rather, it is one of several similar appearing species that co-occur with E. suturalis in the Great Plains and sometimes resemble it due to their large size, sulcate elytra, and occasional presence of a similar reddish-brown sutural stripe. From these species, E. suturalis is at once distinguished by its broadly explanate (flanged) pronotum and laterally carinate, distinctly flattened elytra. This individual clearly exhibits more rounded elytra and as best as I can tell keys to E. hispilabris – distinguished from E. acuta and E. obscurus by possessing a normal first tarsal segment (not thickened apically) on the foreleg (Bennett 2008). Presumably this and the other related species of Eleodes also possess chemical defenses similar to E. suturalis – an example of Müllerian mimicry where multiple species exhibit similar warning coloration or behavior (in this case headstanding) along with genuine anti-predation attributes.
Photo Details: Canon 50D (ISO 100, 1/250 sec, f/14), Canon 100mm macro lens, Canon MT-24EX flash (1/4 ratio) w/ Sto-Fen diffusers. Post-processing: levels, unsharp mask, slight cropping.
Bernett, A. 2008. The genus Eleodes Eschscholtz (Coleoptera: Tenebrionidae) of eastern Colorado. Journal of the Kansas Entomological Society 81(4):377–391.
Wrigley, R. A. 2008. Insect collecting in Mid-western USA, July 2007. The Entomological Society of Manitoba Newsletter 35(2):5–9.
Copyright © Ted C. MacRae 2010