| About Dance Flies |
Dance
flies exhibit unique mating behaviors, and have been
the subject of a number studies seeking to understand the
operation of sexual selection. In “typical” dance
flies, males capture (but do not eat) insect prey, then form
specialized aerial mating swarms. Females fly into the swarm and choose
a mate, which then offers the prey as a nuptial gift for
the female to feed on during mating. Unlike related empidoid flies,
in which both sexes are predatory, many adult dance flies feed mainly
on flower nectar and eat insect prey only during mating.
This presumably makes females dependent on males for protein
to
complete egg development. These behaviors have probably
heightened the strength of sexual selection for dance flies, and led to
the evolution of unusual structures and behaviors for attracting mates
(see Morphology).
There are many variations on this typical set of behaviors. For
example, some groups do not form aerial swarms or present nuptial
gifts. In several groups, males are choosy, and swarms are
composed mainly of conspicuously marked females advertising to males. In other
species, males give the female non-edible gifts of dried insects
or plant parts. "Balloon flies" (certain species of Hilara and Empis) present as a nuptial gift a balloon made of silk or froth, which may be empty or contain a small insect.
Empis aerobatica (Photo: E.M. Fisher)
|
