This unusual looking bug is a female Scorpionfly. Despite their ominous sounding name, these insects do not sting or bite. The name comes from the extended abdomen of the male that curls up and over the Scorpionfly’s dorsal side. The male’s abdomen is terminated with a feature that looks superficially like the stinger of a scorpion.
I have only ever encountered these insects in the mid-October to mid-November time frame. As it turns out, this is the time of the year the subterranean juveniles emerge as adults. The adults quickly court, mate, and lay their eggs before the winter cold sets in.