Figure 1. Female house fly. Image courtesy of Mukund Madhav
Length: Adult house flies are 5-8 mm long
Thorax: Dark-grey in colour with 4 black stripes
Abdomen: Dull, yellow or partially yellow with a dark median line
Eyes: Female: Widely separated by an ovoid frontal stripe
Male: Separated by a narrow frontal stripe
Larvae: Mature larvae are over 10 mm long, smooth and pale yellow to creamy white
The life cycle of the house fly has four stages: egg, larva, pupa and adult. Each female lays over 500 eggs during her lifetime in batches of approximately 100 in manure and rotting food waste (Figure 2). Cattle feedlots and dairies can provide ideal fly breeding conditions.
Larvae develop over 4-7 days before moving to a drier area to form a dark brown protective pupal case around the developing fly. After a few days the adult fly hatches from this pupal case, mates, lays eggs and the cycle starts again. The cycle from egg to adult can be completed in as little as seven days in warm, moist conditions.
This short developmental period, and the large number of eggs produced per female, means that adult populations can build up rapidly. It has been estimated that 1 kg of manure can produce up to 10,000 flies.
So, why aren’t we knee-deep in flies? Factors that limit fly numbers include the moisture content and temperature of the manure, seasonal influences, feedlot management practices and natural enemies such as predators and parasites.
Figure 2. The life cycle of a house fly. Image courtesy of the Queensland Department of Agriculture and Fisheries
Adult house flies are often seen resting on fence posts and railings (Figure 3), vegetation, and inside feed processing areas and offices. House fly larvae grow in non-compacted cattle manure and feed waste. Major problem areas in cattle feedlots include areas where moist manure or excess feed builds up e.g. under fence lines, in sedimentation systems, drains and hospital areas.
House fly numbers increase with increasing temperature and moisture, usually reaching peaks in spring and autumn and after summer rains. Any rain during the summer months will significantly elevate numbers of flies for up to 5 weeks after the rain.
Figure 3. House flies on a fence. Image courtesy of Peter Green, Department of Agriculture and Fisheries
House flies prefer moist locations on cattle and will feed from secretions around the eyes, nose and mouth, causing tail swishes, ear flicks and head tosses.
Adult house flies can transmit human and animal diseases and food contaminants.
Figure 4. House flies annoying cattle. Image courtesy of Jerry Hogsette, USDA.
For more information on house fly treatment and management see the following links.