Aficionados of Bug of the Week have noticed several episodes missing in the Bug of the Week Archives prior to 2012. These lost episodes vanished with a change of servers and a defunct video camera. Through several strokes of good fortune, many of the lost episodes have been found and will reappear from time to time, especially when bug activity grinds to a virtual halt as autumn turns to winter. Here is one such lost episode. In a classic fairy tale, a somewhat forgetful Little Red Riding Hood fails to recognize her grandma but comments on the remarkable size of her teeth. Unfortunately, grandma is a large wolf and Red soon has a much closer look at the fangs than she might have imagined. In this week’s Bug of the Week tale, the rejoinder to “My, what a long tail you have little wasp” is “All the better to sting you with my dear”. For you see, the wolf in our tale is the American pelecinid wasp, Pelecinus polyturator, and Little Red Riding Hood is the subterranean larva of a June beetle about to be parasitized.
White grub larvae such as this one are food for the developing larvae of the pelecinid wasp.
The American pelecinid holds a unique place among its other waspish relatives in that it is one of only three species in its genus and family, a true oddity in the diverse world of insects. It ranges from southern Canada to Argentina, where it inhabits forests rich in decaying organic matter. The larvae of May and June beetles, called white grubs, thrive in nutrient rich decomposing vegetation and are the food source for larvae of these remarkable wasps. The female American pelecinid spends much of her time searching the forest floor. Using cues that we do not fully understand but reckon to be sounds or odors, she detects the location of the beetle grub in its subterranean burrow. She thrusts her remarkably long abdomen into the soil, finds the beetle grub, and deposits an egg on the skin of her victim. One account reports that beetle grubs as deep as five centimeters underground may not escape the tail of this clever parasitoid. The egg hatches into a larva and the tiny maggot-like insect bores its way through the skin of the beetle grub. Once inside, it consumes the grub, alive, from the inside out. With the host consumed and development complete, the larva molts into a pupa. The transformation from pupa to adult takes place in the pupal case, and soon the pelecinid wasp emerges from the soil to feed on nectar from nearby flowers. Rich carbohydrates from nectar power the wasp’s hunt for beetle grubs. As lethal as the pelecinid wasp is to white grubs, it lacks a stinger and is unaggressive towards humans.