 |
Dance Fly - Rhamphomyia longicauda - Male and Female Specimens Order Diptera / Suborder Brachycera / Infraorder Muscomorpha / Family Empididae -- balloon flies, dance flies Live adult dance flies photographed in the wild at Winfield, Illinois, USA. Size: I have accurately measured: Female 11mm head to wingtips, male 10mm. |
|
|
|
Dance flies are known for their mating swarms, in which large numbers flies, sometimes all of one gender, fly up and down in a defined area. These swarms sometimes occur during daylight, but most often at dusk when they are very difficult to see. Male dance flies of some species are known to capture smaller insects and wrap them in silk, then fly about offering the prey to receptive females in the swarm. They have even been known to offer empty balls of silk in an effort to deceive females into mating with them. It is not known how often this practice is successful, however, one would think evolutionary pressures would have eliminated the deceptive strains were it not a viable reproduction tactic. Females in the swarm are similarly engaged in deception: they pump up air sacs in the abdomen, ostensibly in an effort to fool the males into thinking they are bulging with ripe eggs. The fringed legs are said to enhance the effect. [1] However, fig. 4 reveals the female in dancing flight holds all of her legs akimbo, which looks to me like she is just trying to look as large as possible, much like a cat fluffs its fur when threatened.
Species epithet
longicauda, from the Latin "long tail." |
Figure 2. Teneral female in the process of unfurling her wings;
eponymous ovipositor is clearly visible upper left of center.
It is more than superficially reminiscent, to me, of the same gear on some robber flies in
Efferia.
I wonder if these flies copulate tail-to-tail as do the
Asilidae ?
Then there are those three
ocelli between and
behind the compound eyes, much like many
Hymenoptera.
Figure 3. Ventral view shows wings longer than abdomen
Figure 4. Female in flight reveals how the legs are held, and
"droop-snoot" ovipositor.
|
|
|
|
 |
 |
 |
|
The American midwest was seeing a population explosion of these flies this spring and early summer
of 2005. Adults of both sexes dance in swarms of several dozen flies at
twilight; their dark colors make them almost impossible to see at this
time of day.
I had to capture several of them with my hand before I could tell what they were. I then noticed them flying about in the daytime, in heavily shaded areas of deciduous forest. My Audubon Field guide says adults prey on small insects, and larvae live in water or decaying vegetation. |
||
 |
 |
 |
References
|
|
|
"..It's the most bizarre insect story I've read: to male Rhamphomyia longicauda, the most attractive female is the one with the fattest abdomen and hairiest legs (slightly different than the situation in Homo sapiens)."