Flies on Fall Flowers (What Time is it in Nature)

Fall is setting in and with it comes a lot of changes across the Prairie Ridge landscape.  Leaves are changing colors, many plants are disappearing, and there are far fewer insects out and about than there were just a few weeks ago.  However, there are still some insects active at Prairie Ridge!  One group, the hover flies, has been especially abundant recently and have been taking advantage of the last of the available flowers before the cooler weather sets in.

Take a look at any Frost Aster or Aromatic Aster at Prairie Ridge and you’re likely to find at least one species of hover fly!  Hover flies belong to the insect family Syrphidae, a huge family with about 6000 species described so far.  Because the hover fly family is so large, there is huge variation among species.  Some hover flies are small and slender while others are big and broad.  However, most hover flies have spots of bright color on them and many species mimic bees or wasps.  Almost all hover flies also share a strange wing vein, called the spurious vein, that no other insects have.

There are quite a few species flying around Prairie Ridge these days and they show some remarkable variation.  This fly is very small, just shy of 3/16th inch:

Hover fly. Photo by Chris Goforth.

Just a few flowers away, however, you might find this much larger hover fly:

Hover fly. Photo by Chris Goforth.

Both of these flies have the characteristic black and yellow patterns you’ll see in many bee and wasp species.  This individual bears a striking resemblance to a Honey Bee:

Hover fly. Photo by Chris Goforth.

On first glance, it is easy to mistake this fly for a bee!  It’s got similar coloration and has a rather fuzzy body.  However, notice that the fly has only two wings.  Flies belong to the order Diptera, which means “two wings.”  Flies have modified their hind wings into structures called halteres, which are thought to act like gyroscopes to let a fly know how it is positioned in the air.  The fly in the photo above also has short antennae of a typically fly like style.  Bees, on the other hand, have four wings and much longer antennae:

Honey bee. Photo by Chris Goforth.

You can also tell the two apart based on how they fly.  Hover flies get their common name from a rather unique flight ability: they can hover in place.  You’ve probably come across these flies before hovering 2-4 feet off the ground and dashing away as you approach.

Many people are scared of hover flies because they either mistake them for bees or wasps or think they can sting, but they are harmless to people.  Hover fly adults tend to feed on nectar and pollen, so you’ll often see them at flowers.  Their larvae feed on a huge variety of things.  Some are detritivores and help break down dead plant materials.  Some species live in water (including the aptly named rat-tailed maggots) and break down aquatic materials in the bottom of mucky ponds.  Still other species feed on dung or plants.  Most hover fly larvae, however, are predators and perform an essential role in controlling populations of plant pests such as aphids.  In fact, many gardeners will plant flowers to attract hover flies and encourage them to lay eggs in their garden so that they can benefit from the natural pest control services provided by the hover fly maggots.

Cooler weather is coming and the hover flies will disappear along with the flowers soon, so come on out to Prairie Ridge in the next few weeks for a chance to see these amazing and charismatic flies.  You may be surprised by the variation and abundance of flies you’ll find out and about!

What Time is it in Nature is a weekly feature highlighting the current plants, animals, and other wildlife at the Museum’s public outdoor facility, Prairie Ridge Ecostation.  Find out more about the natural happenings at Prairie Ridge at our What Time is it in Nature Archive.