Appearance
"Eristalis tenax" is a large, stocky bee mimic. The eyes are marbled in black. Males have hovering displays. The average wing length is 9.75–13 mm and their average wingspan is 15 mm.The exact appearance of the drone fly can vary considerably. The abdomen can vary in color from dark brown to orange. Pigmentation has an important role in the control of body temperature; the black areas down the center of the drone-flies abdomen may absorb solar radiation and so warm the dorsal blood vessel, which is right underneath.
Distribution
The larval form of the drone-fly, the rat-tailed maggot, is found on every continent except Antarctica, and ranges to the highest latitudes in the North. This species is not prevalent in extremely southern latitudes, neither is it common in arid areas of Europe, Asia, and Africa. In the United States, this species is found as far north as Alaska and as far south as California and Florida.Behavior
The larva of "E. tenax" is a rat-tailed maggot, which is saprophagous. It lives in drainage ditches, pools around manure piles, sewage, and similar places where water is polluted with organic matter. The larvae likely feed on the abundant bacteria living in these places.When fully grown, the larvae creep out into drier habitats, and seek a suitable place to pupate. In doing so, they sometimes enter buildings, especially barns and basements of farm houses. The pupae are typically 10–12 mm long, grey-brown, oval, and retain the long tail; they look like a tiny mouse.
The adult fly that emerges from the pupa is harmless. It looks somewhat like a drone honey bee, and likely gains some degree of protection from this resemblance to a stinging insect. The adults are called drone flies because of this resemblance. In its natural habitat, "E. tenax" is more of a curiosity than a problem. Like other hover flies, they are common visitors to flowers, especially in late summer and autumn, and can be significant pollinators. They often feed on the flowers of carrot and fennel.
Under extremely rare conditions, there have been documented cases of human intestinal myiasis of the rat-tailed maggot. Zumpt proposed a hypothesis called "rectal myiasis". During open defecation in the wilderness, flies attracted to feces may deposit their eggs or larvae near or into the anus, and the larvae then penetrate further into the rectum. The larva can survive, feeding on feces at this site, as long as the breathing tube reaches out from the anus, which is quite rare.The eggs are normally laid on surface water and go through three distinct larval stages. The larvae are usually found in still or stagnant water, like water reservoirs or liquid dung. Just before the pupation stage, the larvae leave their aquatic environment.There are still many gaps in the understanding of the drone fly life cycle, and more detailed research is needed.
Reproduction
The larva is aquatic. It has a cylindrical shape with patches of horizontal folds that divide the body into segments. At each of the segments, two rows of flexible hairs are visible. All drone-fly larvae have a siphon on their posterior end that acts as a respiratory mechanism and looks like a tail, hence the common name, rat-tail maggot. The siphon can be several times the length of the larva's body.The eggs are deposited near the surface of foul water or decaying organic material. The eggs are laid side by side, perpendicular to the ground. It is still unknown how long it takes for the eggs to hatch.The larvae are aquatic, but there must be enough solid food for the larva to complete development. This is why they are found in water with high levels of organic matter. The siphon on the back of the larvae remains at the surface of the water while the larva moves throughout the water. This allows for the larva to search for food without having to go to the surface to breathe. It has been reported that the larvae can reproduce by neoteny or paedogenesis, where the larva copies itself. There has only been one observation of this happening.Mating can happen while a pair of "E. tenax" is flying, with the male uppermost, or on the ground while the female fly is resting on foliage. After mating, the adult female lays clusters of about 10 eggs near dirty, contaminated water, sewage, or decomposing organic substances.Food
The diet of "Eristalis tenax" consists mostly of nectar and the pollen of flowers. During the imago stage, the fly drinks mostly nectar, but will take a little water when it is presented.References:
Some text fragments are auto parsed from Wikipedia.