Clown beetle surprise

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.

REFERENCES:

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

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About Ted C. MacRae

Ted C. MacRae is a research entomologist by vocation and beetle taxonomist by avocation. Areas of expertise in the latter include worldwide jewel beetles (Buprestidae) and North American longhorned beetles (Cerambycidae). More recent work has focused on North American tiger beetles (Cicindelidae) and their distribution, ecology, and conservation.
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12 Responses to Clown beetle surprise

  1. James C. Trager says:

    Do you really think it’s Muellerian mimicry among the Eleodes — Or maybe just a behavioral synapomorphy (“synapethy”?) of the genus?

    • While most Eleodes spp. that co-occur with E. suturalis show the headstanding behavior in response to threat, the three mentioned also resemble it in size and coloration (including sometimes possessing the reddish-brown sutural stripe). Assuming that they also possess similar chemical defenses, this seems to meet the classic definition of Müllerian mimicry.

      • James C. Trager says:

        But maybe not, if they are a single lineage within the genus. Just sayin’…

        • Well that could be – I don’t know enough about Eleodes to say whether these particular species form a single lineage or not. The laterally margined vs. rounded elytral character is one of the early choices in keys to the species, but of course that implies nothing regarding lineages. The three species with the rounded elytra seem to be a lot more closely related to each other than to E. suturalis, at least based on subtlety of distinguishing characters.

          Besides, you’re supposed to just say “Cool picture!” :)

          If I’ve mis-characterized this as a case of Müllerian mimicry, I suppose I can live with it.

  2. James C. Trager says:

    Well, it IS a cool picture!

    I took some not quite as good of relatives of this beetle in AZ. Would you like copies for your beetle photo album?

    • Even better, how about sharing them in a little post here? :)

      I do also have photos of true E. suturalis – just not headstanding. They’re interesting nonetheless and will show up here sooner or later (maybe sooner as a followup to this post).

  3. Roberta says:

    I was interested in the common name “clown beetle.” I like it better than some of our local nicknames for Eleodes here in Arizona.

  4. Arthur Evans says:

    I do miss seeing Eleodes out and about here in Virginia. Seeing them in force in southeastern Arizona was like seeing old friends. Once again, nice image and blog. I do marvel at your productivity in the blogosphere!

    I plan to host a beetle gathering here in Richmond next spring-stay tuned!

    • Thanks, Art. I’ll be interested to know the details of your beetle gathering – can’t say for sure I’d make it, but knowing when and where will help with planning if it’s a possibility.

  5. Hi Ted – I’ve not seen this pose in person, but it is amusing. If this is a defensive pose, I have a pretty good guess as to what would happen if the warning wasn’t heeded. ;-)

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