This week’s insect is probably something that most of you have seen but were likely not sure what it was. Most folks mistake them for paper wasps or yellow jackets, but they are quite different. The Scolliidae are external parasites of Scarab beetle larvae. The female will burrow into the soil in search of Scarab larvae. When found she will sting and then lay an egg on the larva (note the picture of a larva with an egg on it).

Adults here in California are normally black with yellow markings, much like some of the paper wasps. Females are rather hairy, robust wasps, that visit flowers when not looking for Scarab larvae. Males are about 1/3 smaller than females, also hairy, and visit flowers but have unique behavior that sets them apart from other wasps.

When looking for females to mate with, males will fly around in a weaving circular pattern, seldom landing. Home owners will notice this behavior and can be alarmed by these large wasps. I would often get calls about this behavior and was always glad to tell homeowners that the males were harmless and just looking for females, and that the females were not aggressive (but do have a powerful sting if picked up) and were doing them a favor by killing some of their june beetles. They were most common in areas with sandy soil, also preferred by Scarab beetles.

Adults are most active in late spring and early summer. Some of the tropical species are quite large and beautifully colored, making them impressive specimens for an insect collection (note the pictures of two females - not black and yellow).