Last September, labmate and fellow insect collecting enthusiast Stephen Penn and I visited the dolomite glades of the White River Hills in extreme southwestern Missouri. Our main quarry was tiger beetles, specifically a disjunct population of the large and impressive Prairie Tiger Beetle (Cicindelidia obsoleta vulturina) that lives only on the glades in this area and adjacent Arkansas. I was hoping to find additional localities for the beetles in the more western parts of the region where it’s precise distribution in Missouri is less well known. First, however, I wanted to make sure the beetle was out, so we started at the westernmost of its known locations—Chute Ridge Glade at Roaring River State Park. As we picked our way through dry-mesic woodland bordering the more open glades, a large, dead chinquapin oak (Quercus muehlenbergii) with sloughing bark caught my eye. One never knows what might be encountered under bark, regardless of the season, and as I pulled away the very first slab of bark I was rewarded with the sight of what must be North America’s most beautiful assassin bug, Microtomus purcis.
Sometimes called the “bark assassin bug”, this species is not quite as large as the better known “wheel bug” (Arilus cristatus) but makes up this by its spectacular coloration—black with the base of the wings prominently marked creamy-white and parts of the abdomen and hind legs bright red. One would think such a conspicuously marked assassin bug with a bite powerfully painful enough to back up its apparent warning coloration could brazenly venture out during the day with little to fear. To the contrary, this species seems best known for its habit of hiding under bark during the day and venturing out only at night, during which time it is sometimes attracted to lights (Slater & Baranowski 1978, Eaton & Kaufman 2007). A majority of BugGuide photos of the species also mention finding them under bark or apparently attracted to lights.¹
¹ I was especially amused by this particular photo for which the contributor states, “While holding it, the bug pierced my finger nail with its proboscis. The pain was searing and I have a small blood stain under the nail.” I’ll admit it—I, too, learned firsthand how painful the bite of an assassin bug can be when I picked one up, in my case Melanolestes picipes, with plans to include it in my Entomology 101 collection.
I, in fact, have only seen this species once before—also in Missouri and again under bark, although that time was during the winter, thus causing me to think this was its overwintering habit. I placed the individual in a glass vial and brought it indoors to “revive” it, but to my disappointment when I checked on it a few days later it was dead. Froeschner (1944) reported this species (under its older name, Hammacerus purcis) was “not uncommon” in Missouri, though apparently confined to the Ozark Highlands south of the Missouri River. Adult records in Missouri extended from September to March, with small nymphs being found during November and December, but BugGuide records include summer months as well. If I want to see this species more than twice in 30 years, I supposed I am going to have to spend more time peeling bark, or checking lights.
Eaton, E. R. & K. Kaufman. 2007. Kaufman Field Guide to Insects of North America. Houghton Mifflin Harcourt, New York, 391 pp. [Amazon preview].
Froeschner, R. C. 1944. Contribution to a synopsis of the Hemiptera of Missouri, Pt. III. Lygaeidae, Pyrrhocoridae, Piesmidae, Tingidae, Enicocephalidae, Phymatidae, Ploiariidae, Reduviidae, Nabidae. The American Midland Naturalist 31(3):638–683 [JSTOR preview].
Slater, J. A. & R. M. Baranowski. 1978. How to Know the True Bugs. The Pictured Key Nature Series, William C. Brown Company Publishers, Dubuque, Iowa, x + 256 pp. [Amazon description].
© Ted C. MacRae 2015