| The metallic golden pubescence
on this fly's thorax and abdomen is really quite
stunning when viewed close-up. The fly is in the
process of sucking out the liquified guts of an
unfortunate Polydrusus weevil, also commonly known
as the "green immigrant." The American midwest is
experiencing a population explosion of these weevils
in the summer of 2005, and the robber flies are
having a field day with them. There are over 7,000
species of robber flies world wide; nearly 1,000 in
North America. All robber flies have stout,
spiny legs, a dense moustache of bristles on the
face (mystax), and 3 simple eyes (ocelli) in a
characteristic depression between their two large
compound eyes. The mystax helps protect the head and
face when the fly encounters prey bent on defense.
The antennae are short, 3-segmented, sometimes with
a bristle-like structure called an arista. The
short, strong proboscis is used to stab and inject
victims with saliva containing neurotoxic and
proteolytic enzymes which paralyze and digest the
insides; the fly then sucks the liquefied meal much
like we vacuum up an ice cream soda through a straw.
Many species have long, tapering abdomens, sometimes
with a sword-like ovipositor. Others are fat-bodied
bumble bee mimics; the effect is quite convincing.
Take a close look at any insect that looks like a
bumble bee if it's sitting on a leaf - chances are,
it's a robber fly. |
