Grubs in a Wasp Nest

In Pests

Grubs in a Wasp Nest:
We recently had a call from a woman who had grubs (see photo) crawling out of beams in her bedroom. She sent pictures in and we (with the help of Killgerm) identified them as a type of Hover Fly larvae called Syrphidae. These in this case almost certainly came from a wasp nest, either still living or dead. In fact the larvae of this type of Hover Fly as well as feeding in and on wasp and bee nests will feed on a wide range of foodstuffs which is broader than those of most other insect groups. There are those which feed on plant and plant products such as sap, species that scavenge on or filter decaying matter (usually in water), species that live in the nests of social insects (bees, wasps and ants), and carnivores, whose main food is aphids. I was called out to a massive infestation in what was ICI in Jealotts Hill, Bracknell where hundreds of these grubs were crawling out of drains into a building looking for safe places to pupate.

The species that is associated with wasp nests is Volucella spp. The female Hover Fly enters the wasp or bee nest, usually at dusk and lays her eggs on the papery outer surface. Even when stung by the wasps female Volucella are able to lay their eggs while dying. The majority of larvae which hatch fall into the vault of the nest below, which is where the wasps throw their dead adults and larvae. The Volucella larvae therefore have a ready-made food store. Some fly larvae enter the interior of the nest where they lie alongside a wasp larva and eat its excretory products. Strangely these larvae are not attacked by the adult wasps.

Treatment is by a residual insecticide spray and if possible food source removal.