The Fly Killer: In the
warm days of spring, flies often emerge by the dozens and buzz around
the windows inside the house. These are cluster flies and parasitize
earthworms. They overwinter inside the walls of houses and emerge
on warm humid days to lay their eggs on the worms. Sometimes they
emerge on the wrong side of the wall. Occasionally, you will find
a fly stuck to the window by the proboscis with a white halo encircling
the body. The fly has been killed by the fungus Entomophthora
and the halo is caused by masses of spores that have been shot off
from the body. Entomophthora attacks many different fly species.
Here, an adult of the root maggot (Delia) has been attacked
by Entomophthora. The fungus is seen bursting out between
the abdominal segments as a spongy mass.