Monday, October 20, 2008

Maggot Mystery

We, the staff at the Francis Beidler Forest Audubon Center, have never claimed to know everything. However, it is a rare day that something is seen or found and nobody in the building can identify it or even point the curious in the right direction. It happened on Friday!

While preparing some vials of scent for the Girl Scouts' Saturday activity on smells, Mike Dawson decided that the Opossum (Didelphis virginiana), which had fallen into the rain-filled garbage can and expired, would make that perfect "foul odor." He had already removed the carcass and relocated to a spot in the forest away from the parking area. In the process of turning over the carcass in search of some "smelly 'possum juice," several creatures dropped out and began squirming on the ground. One of the specimens was brought into the office for identification by the staff. No such luck. The closest anyone came to a descriptive identification was "a sperm on tons of steroids." Spying the specimen this morning in its vial of alcohol reminded us to solve the mystery.

The Drone fly is well-documented in the rest of the world having arrived in North America prior to 1874. We've got to get out of the office more often! According to the North Carolina State University webpage, the rattailed maggots are the little darlings of drone flies, which resemble honey bees in behavior and appearance (though they have but one set of wings). The larvae are aquatic, so it's no surprise that they were in the semi-submerged, dumpster-diving Opossum. The species Eristalis tenax or Eristalinus aenus are difficult to identify in the larval stage. "The cylindrical, grub-like body may be up to 20 mm long with a tail-like breathing tube 30 to 40 mm long. This hard-bodied life stage is resistant to crushing." --NCSU
Copyright © 2005 Lynette Schimming

Until we get a good picture of the larvae, look here.

"Feeding Habits -- These flies are attracted by colorful flowers (especially yellow) as well as by odors of decay. They do not suck blood. Rattailed maggots feed on decaying organic matter in stagnant water or moist excrement." --NCSU. As the swamp is NOT stagnant water and we do not frequent sites of "moist excrement," it might explain why we haven't seen these guys before.

"Life History -- Drone flies have an unusual and little-studied life cycle. The female fly lays 4 or 5 eggs on or near contaminated water, sewage or other decaying organic matter. The larvae which hatch from these eggs are reported to reproduce paedogenetically, that is, each one gives rise to 7 to 30 daughter larvae. This method of reproduction may last for some time, but periodically female and male flies are also produced. Larvae can withstand many adverse conditions but are eaten by other fly larvae, particularly those of the genera Ophyra, Muscina, Phaonia, etc. Pupation usually occurs in a site drier than that in which the larvae developed. The number of annual generations produced is unknown." --NCSU. Are the flies from the other genera, which we think is scientific geek-talk for rival gangs, actually the dimwits of the fly world? Why else would they dine on the young of a species that actively sought out contaminated water, sewage, or moist excrement as choice birthing habitat?

Thinking back, we wonder how this would have worked for us..."Contractions? Honey, would you prefer giving birth at East Cooper Regional Medical Center or the wastewater treatment plant?"

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