2019 January 12
Jeremy Tatum writes: Sher Falls sends a photograph of an insect from Nanaimo in the summer of 2017. While we usually show pictures of recently-photographed invertebrates, we’ll show this one, partly to keep Invert Alert going during the winter months, but also because it is an interesting insect, and to teach me a lesson.
When I first saw the photograph, I took a quick glance at the narrow, constricted abdomen and confidently declared it to be a hymenopteran of the Family Ichneumonidae. Beware of people who confidently identify an insect after a brief glance! It is not a hymenopteran at all – it is a fly! It is a dipteran of the Family Conopidae. My book by Colyer and Hammond with the unlikely title of British Flies says that conopids “often bear a striking resemblance to solitary wasps and other hymenoptera”. Well, I shan’t use that as an excuse, although the insect does do quite a good job of deception.
It is a parasitoid of bees, including honey bees and bumble bees. Apparently the fly attaches itself piggy-back to a bee in flight and lays its egg on the victim. I quote from British Flies: “The larvae are to be found in the front part of the host’s abdomen… Pupation takes place within the larval skin… The pupa occupies most of the abdominal cavity of the host… When the adult conopid emerges, it ruptures the puparium and the enclosing abdominal segments at the same time.”
We don’t know if the fly is aware of the spider lurking under the flower.
Thick-headed Fly Physocephala burgessi (Dip.: Conopidae) Sher Falls