Last spring while hiking the North Fork Section of the Ozark Trail in southern Missouri (Howell Co.), I made sure to check the abundant flowering dogwood (Cornus florida) blossoms that were in gorgeous peak bloom at the time (early May). I’ve learned to check flowers of dogwood whenever I can, as they are quite attractive to a variety of insects but especially those groups of longhorned beetles (family Cerambycidae) that tend to frequent flowers as adults. In the case of flowering dogwood, most of the cerambycids that I encounter belong to two genera: Molorchus and Euderces. Both of these genera are known for their great resemblance to small ants, no doubt representing examples of Batesian mimicry (where a harmless species adopts the appearance or warning signals of a harmful species to gain protection from predators).
Tilloclytus geminatus on Cornus florida | North Fork Section, Ozark Trail, Howell Co., Missouri
During this particular hike I was determined to photograph Molorchus bimaculatus, common in Missouri during early spring on a great variety of flowering trees. On this day, however, the tiny (<10 mm length) beetles were rather scarce, and I had been frustrated in my attempts to get good photographs of the few that I had found. I’ve seen enough of these beetles over the years that I can recognize them quickly for what they are without the need to closely examine every “ant” that I see. So when I saw an “ant” that was too big and convex in profile to be Molorchus I almost discounted it as a true ant. Something about it, however, gave me pause, and when I looked closer I saw that it was, indeed, a longhorned beetle. But, it was not Molorchus, nor was it Euderces. Instead, it was the species Tilloclytus geminatus—an exciting find!
Adults in profile greatly resemble ants of the same size.
Tilloclytus geminatus has been recorded only sporadically from across the eastern U.S., where it has been reared from a variety of deciduous hardwoods (Craighead 1923, Rice et al. 1985). Perry (1975) did report rearing this species from Pinus virginiana (along with several other species normally associated with hardwoods); however, that record likely represents an ‘‘overflow’’ host (Hespenheide 1969) that is not typical of the species’ normal host preferences. I myself had never seen the species until the years after I published my checklist of Missouri cerambycids (MacRae 1994), having succeeded in rearing adults from a variety of previously unrecorded hardwood hosts that I collected at several localities across southern Missouri (MacRae & Rice 2007). It remains, for me, an infrequently encountered species—perhaps part of this a result of being overlooked due to its effective ant mimicry.
The anterior, oblique markings give the illusion of a constricted “waist”, while the posterior, transverse markings resemble the “sheen” of a shiny abdomen.
Unlike Molorchus and Euderces, this species has not been frequently associated with flowers as adults. In fact, the only report I am aware of is that of Rice et al. (1985), who reported adults on flowers of hawthorn (Crataegus sp.). Perhaps this additional find on Cornus is indicative of a true adult attraction to flowers by T. geminatus, although a single adult provides only weak support. However, a related ant-mimicking longhorned beetle—Cyrtophorus verrucosus—has been collected on flowers of roughleaf dogwood (Cornus drummondii) (MacRae 1994) as well as flowering dogwood (Scheifer 1998a). The floral attraction of ant-mimicking cerambycids may be more characteristic of species in the subfamily Cerambycinae, as only one flower record exists (Physocarpus opulifolius) for Psenocerus supernotatus (Wheeler & Hoebeke 1985) and none exist for Cyrtinus pygmaeus, both in the subfamily Lamiinae rather than Cerambycinae and the only other true ant-mimicking species in Missouri of which I am aware.
Craighead, F. C. 1923. North American cerambycid larvae. A classification and the biology of North American cerambycid larvae. Dominion of Canada, Department of Agriculture, Technical Bulletin No. 27 (new series), 239 pp. [Internet Archive].
Hespenheide, H. A. 1969. Larval feeding site of species of Agrilus (Coleoptera) using
a common host. Oikos 20:558–561 [JSTOR].
MacRae, T. C. 1994. Annotated checklist of the longhorned beetles (Coleoptera: Cerambycidae and Disteniidae) known to occur in Missouri. Insecta Mundi 7(4) (1993):223–252 [pdf].
MacRae, T. C. & M. E. Rice. 2007. Distributional and biological observations on North American Cerambycidae (Coleoptera). The Coleopterists Bulletin 61(2): 227–263 [pdf].
Perry, R. H. 1975. Notes on the long-horned beetles of Virginia, part III (Coleoptera: Cerambycidae). The Coleopterists Bulletin 29(1):59 [JSTOR].
Rice, M. E., R. H. Turnbow Jr. & F. T. Hovore. 1985. Biological and distributional observations on Cerambycidae from the southwestern United States (Coleoptera). The Coleopterists Bulletin 39(1):18–24 [pdf].
Schiefer, T. L. 1998a. A preliminary list of the Cerambycidae and Disteniidae (Coleoptera) of Mississippi. Transactions of the American Entomological Society 124(2):113–131 [JSTOR].
Wheeler, A. G., Jr. & E. R. Hoebeke. 1985. The insect fauna of ninebark, Physocarpus opulifolius (Rosaceae). Proceedings of the Entomological Society of Washington 87(2):356–370 [BioStor].
© Ted C. MacRae 2015