A resident in Florida sent specimens of a tiny wasp to the Penn State lab, saying the wasps were infesting his home and that he’d been stung. They represented a puzzling case. “I knew immediately that the wasps were some kind of bethylid, but it’s not a family I’m overly familiar with,” Skvarla says. “I knew bethylids are capable of stinging people, but they’re generally found in leaf litter and away from human habitation, so it seemed odd the client was being stung.”
So, Skvarla got to work sleuthing. Google turned up a paper on a perhaps similar case from Italy in 2014. A copy of 1978’s The Bethylidae of America North of Mexico, by Howard E. Evans, helped confirm the genus of the specimens was Sclerodermus, same as in the report from Italy. But to get the specific identification, Skvarla needed museum specimens of three North American Sclerodermus species. “Using Evans’ Sclerodermus key and the museum specimens, I was able to determine the Florida specimens were S. macrogaster, which is native to the southeastern U.S.,” he says.
But the identification, in this case, represented a first. Sclerodermus macrogaster had previously never been reported infesting a home in North America. Skvarla saw it as an opportunity to dig a little further into the genus, and his resulting short profile of Sclerodermus wasps and the case of S. macrogaster infestation were published in February in the Journal of Medical Entomology.
Sclerodermus are generally small wasps (1.5 to 6 millimeters in length). Two other species, S. carolinensis and S. ventura, occur in the U.S. and Canada (Sclerodermus domesticus is the species previously reported stinging humans in Italy). Species in the group mainly parasitize wood-boring beetles. This behavior leads to the occasional co-infestation of a home in which such beetles are present. Adult male Sclerodermus wasps are both few in number and short-lived: Sex ratios in offspring typically skew 86-97 percent female, and the males live for only about a week, compared to a lifespan of as long as seven months in females. Moreover, the vast majority of the wasps never grow wings, which makes them easily mistakable for ants to the untrained eye.
