Beneficial Invasive Species - Drone fly (Eristalis tenax)

Drone Fly (Eristalis tenax) is a honeybee mimic
Photo by Brad Sylvester, copyright 2011, all rights reserved

We are used to thinking of invasive species as bad things, but the drone fly (Eristalis tenax) appears to be a case of an introduced species that is actually good for the new environment. The only downside that I could find is that if you eat the maggots, you'll get sick... so, please entomophages, leave this one alone.

Bugguide.net tells us that the drone fly also known as the European drone fly, was introduced to the United States before 1874. It apparently found North America to its liking and is now well established from Alaska to Florida and point seven remotely close to being between them.

With a good look at it, the drone fly is relatively easy to identify even though its behavior and appearance mimics that of a honey bee. It is decidedly less hirsute than the average honey bee, for one thing. The drone fly does, however, fly from flower to flower pollinating them as it feeds on nectar.

• See a slideshow of my Drone Fly photos here.

The drone fly is quite common and is responsible for the pollination of many flowers and garden vegetables. Although the National Audubon Society Field Guide to North American Insects and Spiders  says it prefers compound flowers, I found it on a wide variety of plants in my yard.

The Audubon Guide also suggest that the drone fly may have fooled Ovid, Vergil, Solomon and the author of the Bible's Book of Judges (or at least the protagonist of the book, Samson). All of whom represented in their writings what must have once been a common wives' tale that honeybees rose from the carcasses of dead animals. The drone fly, a notorious honeybee mimic, does, in fact, lay its eggs in either stagnant pools or on rotting meat left in damp locations. Someone passing by and not looking too closely might mistake the drone flies, on a lion's carcass, for example, for a swarm of honeybees.

The larva or maggot of the drone fly is called the rat-tailed maggot. it has a long tail-like tube extended from the back of its abdomen that it sticks up through the surface of the stagnant water in which it lives to breathe. The rat-tailed maggot eats just about any decaying organic material that it can find, then crawls out of the water to a more dry area to pupate and become an adult drone fly.

Occasionally, if people drink fetid water or eat spoiled meat containing the egg or larval form of the drone fly, the maggot can actually live in the intestine for a while causing intestinal pain according to at least one report at the website of the Journal of Clinical Microbiology.

The Drone Fly, then, becomes the first invasive species from my yard recorded in this blog.

Quick facts about the Drone Fly (Eristalis tenax)

Life Cycle: Twenty or so eggs are laid in a group in foul water or decaying flesh. When ready to pupate, the larva climbs from the water to drier ground to form a cocoon and become an adult drone fly.  Britain's National Insect Week website says, as I suspected, that drone flies hibernate like house flies, and may wake on warmer days in the late winter.

Diet: Nectar as adults, rotting organic matter as larva.

Range: All of the continental United States, Alaska, and sub-arctic Canada.

IUCN Redlist Status: Prevalent, not-listed

When are they here: Drone flies are present all year round hibernating as adult flies in the winter, and emerging to lay eggs in the spring. Aside from the occasional warm winter day, drone fly adults are active from April through October.