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.

Two-spotted Bumblebee (Bombus bimaculatus)

Two-spotted Bumblebee (Bombus bimaculatus)
Photo by Brad Sylvester, copyright 2011, all rights reserved
For more photos, click here

Growing up in New England with clover in the lawn, I have certainly seen my share of bees. Although I recall that there used to be far more wild honeybees than I see these days, I do still see a good number of bumblebees in my yard. I see them on the flowers of my squash, peppers, chives and many different flowers all over the yard.  (Let me first say some people use bumble bee as two words and some say bumblebee as one word, I’m going to use the latter variant throughout this page.)

I’ve never really looked closely enough to see what species they were specifically, until now. It turns out that there are quite a few different kinds of bumblebees. My Audubon field guide only lists a few, but it can hardly be blamed as it only covers about 550 insects of the 100,000 or so that live in North America. Whatever species they are, they are certainly welcome in the garden because they seem to be doing a pretty good job of picking up where the missing honeybees have left off in terms of pollinating my vegetable gardens and apple trees.

To figure out what species a bumblebee is, you have to look at the pattern of black and yellow on its head, thorax and abdomen. The best reference for common bumblebee patterns that I’ve found online is this chart from Bumblebee.org. Comparing the photos of bumblebees that I took at about 9:30 a.m. on the sunny morning of July 7^th, 2011, with the grass still wet from evening rains, they appear to be of the species Bombus bimaculatus or the two-spotted bumblebee which therefore becomes the third wild species and second insect added to the master list of What Lives in my Yard? There may be other species as well living in my yard, I’ll be more observant from now on and if I spot a different kind, I’ll make a note of it for this blog.

I’ve included a single picture here on this page, but if you’d like to see a slideshow of the other pictures I took of the two-spotted bumblebee, click here. I’m going to try to put up slideshows of most species from now on to give a wider range of views, and talk about identification a little using the photos. Field guides generally have a single photo and it may be hard to identify one you see given individual differences from the single example.  That’s why I try to take photos from a variety of angles if there is any doubt about the species.

Bumblebees, in general, are pretty easy-going and won’t aggressively attack like a yellow-jacket might. If they do, however, bumblebees have the advantage of being able to sting over and over again since they do not leave their stingers in their victims.

The two-spotted bumblebee, according to bugguide.net, has a long tongue, not unlike a hummingbird’s tongue, that is used to sip nectar from inside long tube flowers. The ones I photographed, however, were collecting pollen. In the photos you can see the pollen sacs on their legs are full and yellow with pollen that will be carried back to the hive. Bombus bimaculatus feeds on both nectar and pollen.

Bumblebees live in ground burrows, and experience a near complete hive die-off each winter. Only the queen survives to re-establish the hive in the spring. Interestingly, the queen bumble bee herself will actually go out and collect pollen for the first new worker bee larva in the spring.

The two-spotted bumblebee lives east of the Mississippi River from southern Canada to Florida.