Family: SyrphidaeFamily: Syrphidae
Subfamily: Eristalinae
Length: typically 13-15 mm
Eristalis tenax was first described from Europe by Linnaeus in 1758. Today the species is cosmopolitan, and in North America it ranges from Alaska to Labrador and from California to Florida. It is probably found in all West Virginia counties.
Larvae of Eristalis tenax are typically found in dung.
The adults are usually described as honeybee mimics, and rely on flower pollen as their only source of protein.
Lunau (1988) showed that small yellow spots on certain species of flower serve to trigger the extension of E. tenax's proboscis. Some flower species even have special guide lines to lead the fly to the yellow spots.
Lunau and Wacht (1994) noted that one plant species, Parnassia palustris, has some yellow "false stamens," lacking pollen, that occupy Eristalis tenax, while presumably the fly's posterior end fertilizes the actual, white, stamens. Thus the plant experiences reduced pollen consumption by E. tenax. Lunau had established in his 1988 paper that these flies "cannot be trained to extend their proboscis towards light stimuli other than yellow."
Golding et al. (2001) created and studied films of the flight of Honeybees (Apis mellifera) and of Eristalis tenax. Among the findings of Golding and her co-authors:
"Both Apis mellifera and Eristalis tenax use a near-horizontal stroke plane while foraging that produces less precise flight than does the inclined stroke plane used by Eristalis tenax males when waiting for a mate. Eristalis tenax is certainly capable of more precise movements, and the fact that it does not use them suggests mimicry as a possible reason."
While some have suggested that in color, markings, and morphology, the resemblance of Eristalis tenax to Honeybees is far from perfect, "there is evidence that humans have confused them with honeybees for more than 2000 years." More than one observer has found examples of behavioral mimicry, such as the habit of E. tenax "of rubbing its hind legs together as it flies in a way very similar to that of honeybees cleaning pollen off their legs and storing it in their pollen baskets" (Howarth et al., 2003).
Insects of West Virginia