My experience with cluster flies is mostly confined to admiring
their astounding numbers on the windows all winter.
According to Swan & Papp, 1972. The Common Insects of North
America. Harper & Row, NY. our common species is Pollenia rudis. I have
no information on P. pseudorudis.
P. rudis is known throughout the US, most of Canada, Europe and
Africa. Resembles a larger, darker house fly, clumsy flier with a loud
buzz. Eggs (about 10 mm) are deposited indiscriminately in the soil.
Larva enters body of earthworm (megadrile, not microdrile) where it feeds
for about 13 days and leaves host to pupate in soil. Adult emerges two
weeks later. Four broods/yr, adults often accumulate in attics, closets or
empty rooms in the fall but do no harm (disgusting but harmless). I can
testify that they are able to survive temperatures of -30 degrees C
overnight but they prefer warm sunny windows.
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