This is the fifth installment of “Wasp Wednesday” that treats another kind of insect often mistaken for a wasp. Today we entertain the clearwing moths of the family Sesiidae. Yes, some moths can pass for wasps!
My own experience suggests that sesiids are not terribly common. I have few in my collection and have not often observed them in the wild. Still, at least a few species are abundant enough to be considered pests, with much research devoted to their control, including the production of synthetic pheromones designed to trap adult moths. More on that later.
You are much more likely to see the moths than you are their larvae. The caterpillars of sesiids are borers, so are concealed in stems, roots, vines, or tree trunks for the entirety of their immature lives. You might be lucky enough to see where a caterpillar had been living because the molted pupa skin often protrudes from a hole where the moth exits.
They may be scarce, but clearwing moths are certainly diverse. There are over 1,100 species known (so far), in 120 genera. The narrow forewings, nearly devoid of scales except for the veins and wing margins, are characteristic. The front wings and hind wings connect in the manner of most moths, with a hook-like “frenulum” on the leading edge of the base of the hind wing interfacing with a patch of setae (hairs) on the underside of the forewing, called a “retinaculum.” However, there is also a unique series of scales on each wing that interlock with each other, further securing the wing coupling.
As you would expect, sesiid moths fly during the day, and one is most likely to find these mimics at flowers where they mingle seamlessly with their “models,” real wasps and bees.
I was fortunate enough to spy the orange-and-black specimen above as it flitted about an open field in Colorado Springs, Colorado on October 22, 2011. Euhagena nebraskae (no common English name, sorry) is one of those “clearwings” that actually does have an abundance of scales on the wings. The larvae of this species are known to bore in the roots of evening primrose (Oenothera spp.). It flies in the fall as an adult moth, and the species is known from southern Alberta to Mexico City, west to southern California. My friend Ted MacRae wrote a post on this species in his blog ”Beetles in the Bush”. My guess is that E. nebraskae mimics some kind of small spider wasp in the family Pompilidae.
I found another interesting sesiid back on August 1, 2009 in South Deerfield, Massachusetts. Contrary to its name, the Lesser Peachtree Borer, Synanthedon pictipes, feeds mostly under the bark of wild cherry. The caterpillars seem to prefer areas of the trees malformed from mechanical injuries, fungal infections, or other abnormalities. The adult moths are convincing mimics of a variety of wasps that share a black-and-white color pattern.
Pest species like the Lesser Peachtree Borer require monitoring in orchards where they can be problematic to census by simple observation. Consequently, during the 1970s, efforts were made to create synthetic pheromones (sex scents produced by the female moths to attract mates in this case). This strategy has paid off, and continues to do so. The only drawback has been the notorious persistence of the pheromones, even after washing and cleaning. Many an agricultural entomologist has been embarrassed in public by an entourage of eager male clearwing moths still sensing residual artificial pheromones on his or her person.
Despite the risk of ridicule, I am sorely tempted to purchase a variety of synthetic pheromones if it will result in more photo ops with these remarkable, beautiful insects. I would sure like to see another Glorious Squash Vine Borer, Melittia gloriosa, for example, like the one below from Pima Canyon in Arizona, August 29, 2010.
Sources: Covell, Charles V. Jr. 1984. A Field Guide to Moths of Eastern North America (Peterson Field Guide Series). Boston: Houghton Mifflin Company. 496 pp.
Powell, Jerry A. and Paul A. Opler. 2009. Moths of Western North America. Berkeley: University of California Press. 370 pp.
Moth Photographers Group
San Diego Natural History Museum
”Using Pheromones to Attract Clearwings”.