At first glance it looks like this root-maggot fly (Diptera: Anthomyiidae) was getting fat and happy filling itself with the sweet juices of this young blackgum tree (Nyssa sylvatica, Cornaceae). It was actually getting fat and unhappy as the unfortunate victim of a fatal pathogenic fungus (Entomophthorales: Entomophthoraceae: Entomophthora muscae).
Spores of this fungus can invade flies from a variety of families. The fungus grows internally and ultimately erupts from the abdomen of the insect. Near the end of the infection the fly is driven to crawl to a high point, grasp the surface with its mouth, extend its legs and wings, and finally die. As the fungus bursts outward it releases countless spores that may in turn infect new flies. Fungal activity is highest in the spring and autumn when flies are active and conditions are cool and moist for the fungus to survive in the environment.