We have received a few calls asking about small, slender, almost translucent maggots recently found in abundance on corn leaves and anthers. These are a curiosity but they are harmless to plants or people. These maggots are the larvae of hover flies (also called syrphids), a type of fly often found in agricultural and horticultural habitats. The hover fly adult is often mistaken for a bee, because of yellow and black stripes on the abdomen. But it is a true fly. If you look at the head, you will see the family resemblance. Adults can sometimes be a nuisance because they are attracted to sweat, both for the moisture and for the salt found in it. However, they neither sting nor bite, and pose no threat. They are called hover flies because of their ability to hold their position steady in flight, rather like a hummingbird.
The larvae of syrphids are small, free-living maggots often found in crop vegetation. Some species are quite beneficial, preying on small-bodied pest insects such as aphids. Some species are pollen-feeders rather than predators. Neither feeds on plant vegetation. The syrphid larvae we’re observing in crops at this time of year are most likely in the genus Toxomerus, which feed on pollen. The reports we’ve received have come from late-pollinating corn, where pollen is abundant. Larvae will aggregate on leaves, leaf axils, and tassels – wherever pollen builds up.
Interestingly, field crop entomologists in several neighboring states have also observed unusual numbers of syrphid flied recently. For reasons we don’t understand, it seems to be a regional trend this year.