Explanation of Names
Pollenia Robineau-Desvoidy 1830
6 spp. in our area(1)
, hundreds total. It is possible that all six species are introduced from Europe.
Adult cluster flies resemble house flies, but are slightly larger, about 5/16 inch long, narrower and nonmetallic gray. When at rest, they overlap their wings at the tips, whereas the house fly does not. Also, the thorax is without distinct stripes, contains many short, yellow-golden hairs, and the dark gray abdomen is hairy with light and dark patches of color. When crushed, the cluster fly has an odor resembling "buckwheat honey."
Species identification is usually impossible from images alone and may require seeing
thorax from behind (one species has a pattern only visible from behind)
underside of the wing, near the base, to see if a tuft of small hairs is present (a 1:1 or closer macro may be necessary)
posterior thoracic spiracle (to see color)
closeup of mid femur and tibia (to see small hairs)
. Cluster Flies (Calliphoridae: Polleniinae: Pollenia
) of North America