Houseflies are a well-known pest of farm and home. Believed to have originated in central Asia, the insect expanded its range worldwide long ago as a commensal organism to human populations; the housefly is always found in association with human activity. As the most common species of fly found on livestock farms, they represent both a nuisance and a risk for disease transmission. High-density housing systems and abundant manure production create the ideal conditions for maggot development. In extreme cases, large fly populations can even create public health issues for the communities surrounding a farm.
Life cycle and appearance of House Flies
The adult house fly (Musca domestica) is 6–7 mm long, yellowish-grey to dark grey in colour, with four narrow black stripes on the thorax, reddish-brown eyes and clear, translucent wings. Female house flies will typically only mate once and retain the sperm for future egg fertilization. When protein-rich food is available, she will lay up to 500 eggs in several batches on decaying organic matter, such as food waste, carrion or feces, over the course of three to four days.
Development time for all Musca domestica life stages is temperature-dependent, with maximum egg production and fly development occurring between 25–30°C. The small (1.2 mm), white eggs will only hatch if they remain moist, and creamy-white larvae (3–9 mm long) with a single pair of dark mouth hooks typically emerge from the eggs within 24 hours. The maggots pass through three larval instars until fully grown (7–12 mm), at which point they crawl to a cool, dry place near the breeding site to pupate.
Flies in the pupal stage are oval-shaped, with bluntly rounded ends, about 8 mm long and change in colour from yellow to red, to brown, to black as the pupa ages. New adult flies will emerge as early as two days after pupation (at temperatures above 30°C) or over three weeks later at low temperatures (around 15°C). Adult flies have an average life span of 15–25 days, but can live up to two months in the right conditions.
While the house fly, like other saprophagous, coprophagous or necrophagous flies, does not cause any direct damage to animals or buildings, they are considered a serious pest because:
- They can form flying swarms inside barns and hen houses, making them a particularly annoying deterrent for employees.
- Adult flies can spread many different pathogens from contaminated breeding sites to healthy animals and people over large distances.
- Musca domestica is a confirmed vector for over 100 different pathogens, including viruses (such as the Newcastle Disease virus), bacteria (such as Salmonella and E. coli), protozoan parasites (such as Giardia), and the eggs of many parasitic worm species.