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Don't be Fooled by Fungus Killed Flies

Dori Eder

Photo 1: Fungus killed flies on grape. Despite any circumstantial evidence, they are incapable of damaging plants.

People are finding a curious insect in their gardens and yards now. Grayish black flies, about ¼ inch long, are being found clinging to the leaves and stems of a variety of different plants. Their legs and wings are typically splayed out in odd, unnatural positions. If you watch the fly carefully, you will notice it doesn't move. That's because it's dead - it has been killed by a fungus that is specific to these flies.

This fungus has been particularly common this year due to the abundant rainfall we have experienced throughout much of Minnesota. When seed corn maggot flies become infected with this fungal disease, they usually fly to a plant or other object and climb up. Eventually they die, leaving their legs and wings in whatever position they were in at the time of death. Additionally, their mouthparts are often extended out. In recently infected flies, the abdomen is swollen and whitish, with fungus protruding between the body segments.

When these flies die on a plant that is damaged, it seems reasonable to blame them for this injury. However, seedcorn maggot flies do not feed on plants (in fact there are no adult flies in Minnesota that directly feed on plants). They are just a curiosity and should be ignored.
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