Bristle flies won’t win any beauty contests, but these early spring insects are fairly rare, and worth a closer look.

Flies in the Tachinidae family are parasitic. In the case of this Epalpus signifer, they lay eggs in or on the larva of a Noctuidae family moth (also known as an owlet, cutworm or armyworm). The young fly uses the caterpillar as its foodstore, eventually killing it. Entomologists dispassionately call the caterpillar the “host,” though it’s hard to imagine a parasite would ever be an invited guest. 

As adults, these flies are pollinators. They eat nectar and can be found on dandelions and other flowers. At up to a half-inch long, they can pass for bumble bees. In fact, I found this one on a bank of flowering Oregon grape, among scores of yellow-faced bumble bees.

Adults emerge in early spring. Last year that meant early March; this year, you’ve still got time to see them. They have widely-spread brown eyes. The thorax is tan and the abdomen black, with a distinctive white mark on the hind end.

One study found Tachinidae flies are extremely adaptive, and among the most rapidly diversifying families of not just insects, but of all animals. The 2021 paper says these flies are the most important group of parasitoids after parasitic wasps. 

Stay curious!

See more of Karen’s work here.


Basic information: Accessed 3/7/23.

Academic paper about the rapid diversification of the family: Accessed 3/7/23.