The adult Blue Blow Flies have a dull-colored thorax and a shiny metallic blue-green abdomen. They are about 5/16” long. The head is grey with large red eyes, black sides, and reddish beard. The thorax is dark grey. The legs are dark grey to black and bristly. The wings are clear.
Blue Blow Flies breed almost exclusively in decaying animal matter. Female flies may lay hundreds of eggs during their lifetimes. The eggs require 90% relative humidity to hatch. If enough moisture is present, hatching occurs almost immediately.
The larvae grow rapidly and, when mature, often crawl many feet to pupate in drier places, either in the soil or in crevices of buildings. New adults emerge in 2-3 weeks. They can have several generations per season. Blue Blow Flies are seldom a major pest, but their search for overwintering sites in your barn may cause some concern. Proper disposal of deceased animals will help keep numbers down.
Adult Black Blow Flies are dark green or blue-black on the thorax and abdomen and about 5/16” long.
Black Blow Flies are one of the most common flies associated with wound myiasis (fly larvae (maggots) found in a wound feeding on necrotic tissue), especially in livestock. In cases of myiasis, larvae sometimes cause a bloody discharge, indicating a certain amount of destruction of live tissue.
The larvae normally feed in dead tissue, breeding in carcasses and wounds but they are also common around household garbage cans. The larval stage takes 4-15 days. Growth from egg to adult takes 8-15 days.
Dr. Bill ClymerFort Dodge Animal Health, Dr. Roy EllisPrairie Pest Management, Dr. Kevin FloateAgriculture and Agri-Food Canada, Dr. Robert M. Miller, DVM, Dr. William QuarlesBio-Integral Resource Center. All illustrations 2006 Dr. Roy Ellis.
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