Family Calliphoridae - Blow, Bottle, Cluster and Screwworm Flies
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Calliphorids are usually the first insects to arrive at a fresh carcass
Live adult blow flies photographed at DuPage County, Illinois.

A lovely golden-haired female from Pennsylvania: Cluster Fly Pollenia sp.
Most blow flies lay their eggs almost exclusively in dead or rotting flesh. A few species' larvae are parasitic on bird nestlings, some have larvae that live as internal parasites of mammals; theyare serious pests of livestock, especially in the tropics. They cause myiasis, a condition in which their larvae inhabit the skin or connective tissue of large mammal hosts. Larvae of some bot flies (Oestridae), and flesh flies (Sarcophagidae) also use this parasitic stage. [1].

Calliphorids are usually the first insects to arrive at a fresh carcass, sometimes within minutes of death; they are attracted by the organic odors of  decomposition. Eggs are laid around natural body orifices or open wounds, and the larvae molt and pupate at predictable rates for any given ambient temperature and humidity; it is for these reasons the blowflies are so important in forensic pathology. Maggots (larvae) and pupariums (the hollow cases left behind after the adult fly emerges) collected from a body can be used to determine, sometimes very accurately, the time of death.

Female blow flies require a substantial amount of protein to develop mature eggs within their ovaries. A typical female blow-fly typically lays 150-200 eggs per batch, and up to 2,000 eggs during her lifetime.


Caliphora vicina, present on every continent save Antarctica [1,3]
Blow Fly - Calliphora vomitoria
Blue Bottle Fly - Calliphora vomitoria
Lucilia sericata, the common green bottle fly is slightly larger than a housefly, brilliant metallic blue-green or golden in color, 10-14mm long. Females lay eggs in clutches of about 180 on garbage or carrion. Maggots attain full size in 2-10 days, depending on ambient temperature, then drop to the soil and burrow before pupating. There are many generations per year, the last overwintering underground as pupae [4].
References
  1. Bugguide.net, "Blow Fly Calliphora vicina"
  2. Bugguide.net, "Blow Fly, Calliphora vomitoria"
  3. Eric Eaton, Kenn Kaufman, Field Guide to Insects of North America
  4. National Audubon Society, Field Guide to Insects, Alfred A. Knopf, 2000
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Flies of North America - Order Diptera. Flies are prevalent in virtually all habitats, with over 16,000 species in North America. Flies can be distinguished from all other insects in that they only have one pair of normal wings. Most flies have compound eyes and mouthparts adapted for piercing, lapping or sucking fluids. Insects & Spiders | Flies Index | Syrphidae | Bee Flies | Robber Flies
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