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Dolichopus cuprinus, the Long-Legged Fly

By: Dr. Kelton Welch

April 28, 2021

Here at Ecdysis, we love bugs! For every insect that’s a pest, there are over a thousand that are beneficial to us and their environment. They are not our enemies: they are our partners, our allies, in the effort to regenerate our soils and sustain our lands for the future. This article will introduce you to just one of these important allies.

What’s in a name?

Each species of animal and plant is given a unique scientific name, to help scientists keep track of our planet’s biodiversity and all our allies in the effort to conserve our planet. Scientific names use words from Latin and Greek (and sometimes other languages), and they are usually chosen to represent the organism’s characteristics or the history of its discovery, and you can usually learn what it means by breaking the name down.

This species is named Dolichopus cuprinus (“doe-LICK-uh-pus”), a true fly (Order Diptera) from the family Dolichopodidae. The “dolicho-“ part means “long”, and the “-pus/-pod” part means “leg” or “foot.” The word “cuprinus” means “copper.” So, the fly’s full name basically means “copper long-legged fly.”

Many insects also have common names, which are just simple names people use for easier communication. But historically, people didn’t find a lot of reason for communicating about some types of insects (especially the smallest ones that you can’t see easily); so many insects were never given common names. This means that scientists sometimes make up common names. Dolichopodid flies are usually just called “long-legged flies,” to match the scientific name. That’s a little bit bland though, isn’t it? Personally, I’d like to call it something more vivid, like “emerald fly”.

Look a little closer

Dolichopus is a medium-sized fly: it’s smaller than a house fly, but larger than a midge or gnat. It’s about the same size as a mosquito. But, it’s significantly prettier. That beautiful, metallic color is its signature. Depending on the light, it might look more green or more gold. Most species of long-legged fly have similar metallic colors: green, gold, copper, sometimes a little bit purplish. Some even have a brilliant, sapphire blue color in the right lighting.

Males of Dolichopus have little disc-shaped structures on their front feet, which kind of look like signal flags, or maybe plump little mittens. Those are for getting the attention of the lady flies. The male displays his flags, flaps his wings, and dances a little bit to attract a mate. You might see one scuttling about on the surface of a leaf, then jumping in a quick flight to the next leaf to dance again.

A Dolichopus fly wasn’t always so beautiful, though: it started its life as a white, wiggly little maggot. Then, when it had grown enough, it pupated, just as if it were a caterpillar (but without the silken cocoon that caterpillars often build). Once safely tucked away inside its pupal skin, Dolichopus completely remade its entire body, and emerged as the beautiful, metallic “emerald fly” you see in the pictures above.

An adult male Dolichopus cuprinus under the microscope. Note the “mittens” or “flags” on its front feet, the enormous genitalia curved under its body (kind of like a backhoe), and the bright green-and-gold shimmer (Photo credit: Dr. Kelton Welch, Ecdysis Foundation).

The world according to Dolichopus

Dolichopus is a predatory fly. It captures and eats tiny creatures, like springtails and worms and aphids. Even the maggots are predators, as well, so one Dolichopus will probably eat hundreds of small invertebrates over its lifetime. This makes it an important part of the food web. If we can get our ecosystems back into balance, predators like Dolichopus can prevent creatures like aphids from growing out of control and becoming “pests.”

You probably won’t see Dolichopus in large numbers, but they can be found readily in most places, especially if you look closely at broad-leaved forbs and shrubs. The edges of shelter belts are good places to look: Dolichopus males like to dance about on broad leaves that look out over a lot of open air. They are usually very active flies, and on sunny days, their colors are really resplendent.

Another tiny ally in the effort to keep our planet functioning

So, (1) beautiful, (2) fun to watch, and (3) beneficial for the ecosystem. What more could you possibly want from a bug?

Keep your eyes open in the field, and watch for our tiny, ecological partners, like Dolichopus, playing their parts in our ecosystems.

An adult Dolichopus cuprinus in the middle of skittering across leaves, holding still just long enough for me to take a photo. They tend to be quite active, and quite fun to watch, especially when a male and female find one another and begin to dance (Photo credit: Dr. Kelton Welch, Ecdysis Foundation).


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