The Sand Wasp, an Attentive Mother – Terry Thormin
I went to Little River Pond about two weeks ago and noticed that the Sand Wasps, Bembix americana, were still flying. With the warm weather we are getting it is possible that they are still around and might continue for a while yet.
I have always liked these beautiful wasps. They are found almost anywhere there is bare soil, although they particularly like sandy areas. Unlike yellow jackets they are not aggressive and you would probably have to step on one with bare feet to get stung. They are members of the family called Digger Wasps (Crabronidae) and like most members of this family they dig nests in sand or soil. They are also solitary nesters, that is, each female digs its own nests. In ideal habitat though the nest sites can be so numerous it almost appears to be a colony. Two years ago the sand dunes at Point Holmes in Comox were thick with these wasps and I estimated several thousand in a narrow strip about 3 to 4 meters wide and about 100 meters long. Since then numbers have not been as great, but they are still fairly common.
Sand Wasp on a log
The female Sand Wasp will dig a nest hole in the ground and lay a single egg in the hole. She then catches and stings a fly which she drags, still alive but paralyzed from the sting, into the hole, and then she closes the hole with sand, pebbles or dirt. When the egg hatches the larva feeds on the paralyzed fly. At regular intervals the female will provision the nest site with another fly, each time closing the hole again, until the larva is finally large enough to pupate and turn into an adult wasp. This is referred to as progressive provisioning and is considered to be a more advanced evolutionary stage in nesting behavior. With multiple nest sites each female must be very busy attending to her young during the summer, and a large group of Sand Wasps in one area must put a considerable dent in the local fly population.
A female Sand Wasp digging a nest hole
Adult Sand Wasps, unlike the larvae, feed on the nectar of flowers and will go to a large variety of flowers. In this photo you can see the large mandibles that distinguish the females from the males. From what I have read another difference is that the females are white and the males are yellow, although the yellow will turn a pale blue with age. Bugguide however has photos of individuals labeled females that are clearly yellow. Something else to sort out.
A female Sand Wasp nectaring
A yellow male? Sand Wasp