Merck Manual

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Professional Version

Filth-breeding Flies of Animals


Jan Šlapeta

, MVDr, PhD, GradCertEd (Higher Ed), Sydney School of Veterinary Science, The University of Sydney

Reviewed/Revised Aug 2022 | Modified Oct 2022

The following adult dipterans are often referred to as filth-breeding flies: Musca domestica (the house fly); Calliphora, Phaenicia, Lucilia, and Phormia spp (the blow flies or bottle flies); Sarcophaga spp (the flesh flies); Fannia spp (the little house flies); Muscina spp (the false stable flies); and Hermetia illucens (the black soldier flies). Large populations of these adult flies are often found around facilities associated with animal feces. Larval stages may be associated with skin wounds contaminated with bacteria or with a matted hair coat contaminated with feces Facultative Myiasis-producing Flies of Animals Facultative myiasis-producing flies of veterinary importance covered in other chapters include Gasterophilus spp in horses, Oestrus ovis in sheep, and Cuterebra spp in dogs... read more . The life cycle of M domestica will be used as a representative example of the life cycles of the assorted filth-breeding flies.

The house fly is commonly found around production animals and poultry operations, where it readily breeds in accumulating manure sources. It is a medium-sized (as large as 9 mm), grayish fly with four dark thoracic stripes and sponging, nonbiting mouthparts designed for sucking semiliquid food (there are no mandibles or maxillae). The labium is expanded into two labellae that can transfer fluids and semifluids.

After oviposition, the creamy-white, banana-shaped egg (~1 mm long) hatches in 6–12 hours in optimal conditions. The eggs are not resistant to drying, and few appear to survive temperatures >40°C or < 15°C. Larvae may develop in a few days to 3 weeks, depending on the temperature and availability of food. When temperature for larval development is optimal (~36°C), the larvae develop to pupae in ~6 hours. Pupae persist 4–5 days in warm weather. After the adults emerge, the flies search for food and copulate after a few days. The life cycle is usually completed in ~3 weeks, although it can be completed in as little as 10–14 days under favorable conditions. In temperate climates, it is thought that house flies overwinter as pupae.

Pathology of Filth-breeding Flies of Animals

Even though these flies do not feed on blood, annoyance due to their movement on and off animals can lead to reduced performance. In addition, they have been implicated in the transmission of numerous pathogens (helminth, protozoan, bacterial, and viral) of humans and other animals. Large populations of these adult flies often are found around poorly managed production animals or poultry facilities and become a public annoyance. These are synanthropic flies, ie, they are often associated with human dwellings. The flies are “vomit drop” feeders and fly from feces to food, transmitting bacteria on their feet and within their disgorged stomach contents.

Diagnosis of Filth-breeding Flies of Animals

All adult filth-breeding flies have similar sponging, nonbiting mouthparts, designed for sucking semiliquid food. The identification of adult flies is best left to a specialist. House flies are medium-sized, grayish flies with four dark thoracic stripes. A preliminary identification of blow flies or bottle flies may be made on the basis of the metallic coloring of the adults. Flesh flies are medium-sized, grayish flies with a checkerboard abdominal pattern.

Treatment and Control of Filth-breeding Flies of Animals

  • Sanitation program and feces management to discourage fly breeding

  • Insecticides and fly baits are supplementary to good sanitation practices

A thorough sanitation program is necessary to control fly populations in and around production animals and poultry facilities. All manure accumulations should be removed at least twice a week or handled properly, if stored on the premises, to minimize fly breeding. If solid manure management practices are applied, efforts should be made to decrease manure moisture. If a liquid manure pit is used, manure should not be allowed to accumulate above the waterline, either floating or sticking to the sides, because this is an ideal site for fly reproduction.

Insecticides should be considered as supplementary to sanitation and management measures aimed at preventing fly breeding. Residual sprays providing 2–4 weeks control with one treatment may be applied to fly-resting surfaces. Space sprays, mists, or fogs with quick knockdown but no residual action can be used for immediate reduction of high numbers of adult flies.

Other measures for control of adult flies include use of insecticide resin strips or various fly baits. These measures can be applied directly to fly-breeding sources; however, this should be considered only for fly-breeding spots that cannot be eliminated by normal sanitation practices.

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