Entomophthora  muscae
Entomophthora muscae
Fungus attacking fly
Photo © George Barron
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.