Published in Yard & Garden Brief, November 1999
In early summer, especially after rainy periods, a certain type of fly is commonly found clinging to the leaves and stems of trees, shrubs, flowers, and other vegetation. Although they appear to be eating or sucking the leaves or needles, these flies are actually dead, killed by a fungal disease.
These flies are seed corn maggot adults; the larvae are maggots which live underground, feeding on the roots of vegetables. The adults are dark gray and resemble house flies but are smaller and more slender. Although the flies appear to be damaging or even killing, leaves or branches, they are harmless to plants. They have sponging-sucking mouthparts which do not injure plants.
When seed corn maggots become infected with this fungal disease, they typically fly to a plant or other object and climb up. Eventually they die, often with their legs clinging to the vegetation in odd, unnatural positions. Their mouthparts are often extended out. In recently infested flies, the abdomen is swollen and whitish, with fungus protruding between the body segments.
Although other insects are susceptible to disease, seed corn maggot adults are particularly conspicuous in the landscape. However, it is pure coincidence if a plant where a seedcorn maggot adult has landed is also damaged. These flies are a curiosity and no action is necessary against them.