Length: Adult bushflies are 4-8 mm long
Thorax: Grey in colour with 2 dark stripes that split into 4 near the head
Abdomen: Female: Grey/black
Male: Orange/brown with a dark base and a black dorsal stripe
Eyes: Female: Eyes don’t touch in centre
Male: Almost touch in the centre
Larvae: Mature larvae are 7-10 mm long, smooth and creamy white
The most obvious difference to house flies are the 2 stripes on the thorax instead of 4 (Figure 1).
Figure 1: Bushfly, Musca vetustissima, showing 2 dark stripes on the thorax. Image courtesy of Mark Schultz
Biology of bushflies
The life cycle of the bushfly has four stages: egg, larva, pupa and adult. Each female bushfly can lay up to 5 batches of 50 eggs in moist cow dung. Bushflies also breed in the dung of native animals, horses, sheep, dog and other animals. However, because of the volume of cow dung available in grazing areas of Australia, cowpats are by far the major source of bush flies. Bush flies generally do not breed in feedlots, but they may enter feedlots in large numbers to feed on cattle eye, nasal and other secretions. This can cause significant annoyance to cattle and has been associated with outbreaks of pinkeye in feedlots.
Eggs are laid in fresh cow dung and develop rapidly (7 hours at 32°C). Larvae take 2.5 to 3 days (at 32°C) to develop within the dung pat. The last larval stage leaves the dung to pupate (form a dark brown protective case around the developing fly) and will bury itself in dry soil taking from 3 days (39°C) to 18 days (18°C) to emerge into an adult fly. Adults take about 3 days to become sexually mature.
Adults are active in temperatures between 12 and 35°C. At temperatures higher than 35°C, flies will generally avoid heat and move into more shaded areas.
Adults tend to avoid heavily forested areas and prefer open pasture settings. Two patterns of seasonal abundance are known:
Bushflies are generally attracted to the eyes, mouths and sometimes the wounds of domestic animals as well as humans. Adults can be seen feeding on the tears, saliva, blood, serum and pus from large animals.
The seasonal changes that occur in pastures influences dung composition, which therefore influences the numbers of bushflies. In a pasture, during times of new spring growth, cattle void dung that is very liquid and homogeneous, with bushflies tending to avoid this type of substrate. As vegetation matures within a pasture, cattle dung becomes more fibrous with undigested plant material, dung forms in higher mounds with a stiffer consistency. Bushfly adults prefer this substrate, producing larger numbers of flies. Monsoonal rains in summer can increase the suitability of dung for fly breeding over a large part of the north and central Australian cattle production areas and are often followed by increase in fly breeding and epidemic numbers of bushflies.
Adults can aid in the formation of skin sores. Bushflies are also known to carry various food-borne pathogens, including Escherichia coli and Shigella.
For more information on bushfly treatment and management see the following links.