Fly Worry

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Musca spp. flies, of the family muscadiae are classed as 'nuisance flies' and 'biting flies' as they can cause fly worry in animals, particularly livestock.
These flies not only cause fly worry but can be vectors for disease. Muscadiae flies can transmit the viral disease coxsackie, enteroviruses and poliomyelitis, as well as African Horse Sickness. They carry the bacteria Bacillus anthracis, E.coli, Salmonella, Shigella and Moraxella bovis and are intermediate hosts for helminths such as Habronema in horses, some poultry tapeworms, Parafiliaria and Thelazia in cattle.
Not only do Musca flies carry these diseases, they also feeds on secretions from the eyes, nose and mouth as well as blood left in wounds by other flies.
There may be more flies in unhygienic conditions as flies are attracted to and will lay eggs in manure.

Animals become so distressed by the presence of flies swarming around them, particularly their head and eyes, that they will eat less and therefore have a reduced weight gain and there will be production losses. Animals may move suddenly and try to escape them, causing self trauma. This may then predispose to blowfly strike, secondary bacterial infection and other conditions.


Any animal or any breed, age or sex can be affected by fly worry, particularly so if the environment is unhygienic.

Clinical Signs

Production losses, reduced weight gain, reduced milk yield and notable signs of fly worry such as tossing of the head, sudden movements and reluctance to eat. There may also be signs of self trauma such as 'broken head' in sheep and other abrasions on the animal.


Clinical signs and visualisation of flies on the animal or around the animal.

Treatment and Control

It is vital to ensure fly control in breeding and resting sites (to reduce the source). Good sanitation is vital to reduce the area of breeding sites, such as collection of dung into heaps, spraying the surface of dung heaps with insecticide to kill surviving adults and larvae. Spraying resting sites such as farm buildings etc with insecticide is also important.

Fly control on the host is imperative and a wide range of products are available in pour on or spot on forms and even as insecticide impregnated ear tags. These products have nil or short withdrawal periods, which is needed for milking animals or animals going for slaughter.

Fly Worry Learning Resources
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Test your knowledge using flashcard type questions
Sheep Medicine Q&A 08


Fox, M and Jacobs, D. (2007) Parasitology Study Guide Part 1: Ectoparasites, Royal Veterinary College.
Quinn, P.J., Markey, B.K., Carter, M.E., Donnelly, W.J., Leonard, F.C. (2007) Veterinary Microbiology and Microbial Disease, Blackwell Publishing.'

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