A Texas Standard listener wanted to know more about hover flies – also sometimes called flower flies or syrphid flies because they’re in the family Syrphidae – particularly why they buzz like a bee.
Wizzie Brown, our go-to insect expert, said that for any insect, the buzzing sounds are created by the wings – essentially displacement of the air by the wings.
“If you think about smaller insects, they’re going to beat their wings more quickly. And so that’s going to be at a higher frequency, whereas larger insects are going to beat them typically more slowly,”said Brown, a program specialist with Texas A&M AgriLife Extension Service. “The human range of hearing is 20 to 20,000 Hz. And so where that insect sound falls, if it’s in that range, then we’re going to be able to hear it. And then, of course, as you get older, you might start to lose your hearing. And so that range is going to decrease usually at the higher levels.”
Hover flies vary in size and habitat, and a lot of them mimic bees and wasps – but unlike four-winged bees and wasps, flies have only two.
“How I always find out if something is a syrphid fly, other than if it looks like a beer or a wasp and only has two wings, if it’s one of those weird ones – they have what’s called a spurious vein,” Brown said. “And I essentially refer to that as the ‘vein to nowhere’ because it just kind of goes off of the wing and it just kind of randomly stops in the middle of the wing for no reason. And so that’s kind of what you look for.”
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Brown said that what she really likes about the syrphid fly is the larval stage, which is the immature stage.
“Most of these are going to kind of have a maggot-like body like we think of with normal flies, but they’re generally a different color. So most maggots are like that creamy white color, but with syrphid fly maggots, they’re usually like browns, greens,” she said. “We have one here that’s common in Central Texas that’s like a green with like a whitish pink stripe. Those are going to be typically predators.
“But we also have some aquatic species that actually live in kind of gross areas. So they feed on sewage and wet fecal material. And those maggots are going to look a little bit different because they have this really long tail that comes off of the tip of their abdomen, and they’re actually called rat-tailed maggots. And that long tail is kind of like a siphon tube or a snorkel that they’ll use to stick out of whatever funk they’re living in and eating. And that’s how they actually can breathe. So they’re breathing out of their butt, pretty much.”
The more common green flies feed on aphids and other small soft-bodied insects and typically have five to seven generations per year. It usually takes them two to four weeks to go from egg to adult stage, Brown said, and in the larval stage they can eat anywhere from 100 to 400 aphids.
“The adult flower flies are going to feed on honeydew nectar and pollen, but they are still beneficial – not beneficial as predators in the adult stage – but they are beneficial as pollinators. So still super good,” she said.
