Drone Flies: flies in (really good) bee costumes

Eristalis flavipes.
Male Eristalis flavipes? Not only looks like a bumble bee, it moves around like one, both in flight and nectaring. Photo by Charles Matson, Bugguide.net.

By Vicki Wojcik, Pollinator Partnership

The diverse group of flower flies and hover flies (family Syrphidae) includes many successful bee mimics. Drone flies (members of the genera Eristalis) masquerade as bees with various body forms and striping patterns that are almost perfect matches to many common bee species. Often very effective pollinators due to their hairy bodies, flies have keystone roles in many of ecosystems where they occur. Flies are also the dominant (and in some cases only) pollinators of key crops and foods like coffee, chocolate, tea, bananas, and mangoes.

So why would a fly want to be a bee? While they are surely happy in their species roles, pollinating beautiful wildflowers in gardens, meadows, and wildlands, and providing us with wonderful fruits and kitchen staples, there is one thing flies cannot do that bees can – sting!

A sting is a wonderful thing if you are small, soft, and tasty to the many birds, lizards, frogs, and small mammals that you share your ecosystems. If you do not have a sting to keep these predators at bay, you have to be a bit more creative. Outsmarting your adversary might just work. In fact, so many unarmored and undefended species use trickery to stay out of harm’s way scientists have given this system a name: Batesian mimicry. Famous English naturalist Henry Walter Bates came upon this concept during his work in the Brazilian Amazon where he observed numerous non-toxic butterflies that looked identical to a few very potent types.

Mimics take advantage of other species’ reputations as dangerous and difficult to swallow. Getting stung will surly make you think twice about eating a bee; and flies that look like bees can get a free pass. Drone flies have taken Batesian mimicry to the next level.

Eristalis texans.
Eristalis tenax. Photo by Stephen Cresswell.

Eristalis flavipes.
Eristalis flavipes (male). Photo by Tom Murray.

Helophilus sp.
Helophilus sp. (female). Photo by Tom Murray.

Eristalis tenax, the common drone fly, can even fool trained scientists when it flies by. Not only does this species look like the honeybee, it has changed its behavior to fly more like a bee by moving back and forth between flowers rather than hovering in place.

Mimicking is a strategy that works well, and many other flies use this survival strategy. Some bee mimics look like leaf cutter bees in the genus Megachile; Eristalis dimidiata is a great example. Some species, like Eristalis flavipes look like bumblebees, complete with fuzzy abdomens and thoraxes.

Flies in the genus Helophilus mimic another hymenopteran group with a stinger, the wasps. The most wasp-like of these are in the genus Helophilus, mimicking the more painful stings of the Vespidae. Helophilus fasciatus copies the colors and patterns of a common yellow jacket, complete with longitudinal bands of yellow and black on the thorax, and transverse stripes on the abdomen. Any predator that has had a previous Vespula spp. encounter surely will not approach this fly!

Drone flies, and other bee and wasp mimics, visit flowers in search of nectar to fuel their flight. They are hungry for pollen, especially the females. Like most flies, they have sucking mouthparts that only enable them to drink fluids, but they can absorb pollen grains along with the nectar. Their stomach juices can dissolve some of the outer coating of the pollen and release the nutritious proteins inside. It is known that females need these extra proteins to make eggs. Drone flies are frequent visitors to a great variety of flowers, and since they have several generations each year, they continue visiting flowers through the seasons from early spring to late fall, switching from one type of bloom to another as flowers come and go.

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