Blow flies are closely related to houseflies and are generally classified as nuisance pests that breed in unsanitary sites and badly managed food-handling areas. Though the insects do not bite, they can transmit diseases from filth. Blow flies are also commonly referred to as blue bottles, and the scavenging pests are frequently found in and around homes.
Adult blow flies range in length between 0.75 and 1.25 cm long and have dark green/blue, metallic bodies with black legs. Certain species have distinct orange-coloured heads, yellow mouth parts or a bronze colour. The flies lay their tiny, white to cream-coloured eggs in large masses. Eggs are elongated with slightly tapered ends. The emerging larvae have pointed heads.
Blow flies have a lifespan of two to eight weeks and lay thousands of eggs in masses of 40 to 1,000 during this periods. Groups of females are usually responsible for larger egg batches. Under warm and humid conditions, the eggs hatch within 24 hours. The emerging maggots are mature in four to 10 days. The developmental rate is accelerated under optimal feeding conditions. The mature larvae take about a week to pupate, retreating to dark and secluded areas in the house, and then emerge as adults. The females start to lay eggs within a week.
Blow flies occur throughout the UK and in all temperate regions around the world. The flies are attracted to decaying organic matter and frequently infest animal wounds. Dirty sheep are a favourite breeding ground. In domestic settings, the flies are found around decaying fruit, pet waste, rubbish and other refuse. The flies do not infest hygienic areas or healthy tissues. Dead animals such as birds and rodents around the house or in chimneys or dead mice in walls can lead to flies in the house. A leak in sewer pipes is often found to be the cause of sudden appearance of blow flies.
Maintaining sanitary conditions in and around the house is the best way to control blow fly populations. Do not allow rubbish to accumulate for too long and make sure bin lids close properly. Check drains and sewer pipes for damage. Poorly maintained compost piles or pet faeces on the property also encourage flies. Install fly strips around windows to capture flies. Recommended insecticides for use inside the house include products containing cyfluthrin, permethrin or deltamethrin.