COUNTRYSIDE NOTES SEPTEMBER 2019 FLIES

One of the drawbacks of an English summer is flies and there have been plenty of them about this year. Apparently there are more than five thousand species in Britain. They vary greatly in size; some are useful but most are not. At least in England we’re not plagued with midges or at risk of contracting malaria from mosquitoes although, having said that, it was rife in England’s marshes and fens until the late nineteenth century. A few, such as hover flies, which look like small wasps and dart about as well as hovering, are beneficial to plants as pollinators while lacewings feed on aphids, mealy bugs and spider mites. Most flies however are potentially harmful. The most familiar are house flies which show no inclination to go back outside once indoors. They are major carriers of disease being attracted to food and faeces, are annoying when they settle on you, and appear to be immune to fly spray (but not a swat!). Bluebottles/blowflies, which lay their eggs on carcases, are also horrible but at least they oblige by going out the window when you open it. Fruit or vinegar flies also come indoors to aggravate us. In winter cluster flies hibernate in lofts. It is they that appear from nowhere indoors on a sunny winter’s day. Minute yellow swarming flies often hibernate with them.
Outdoors in summer there are black flies which swarm round our heads and sometimes bite and several species that plague livestock. So called horse flies inflict very painful bites to both animals and humans. Males actually feed on nectar and pollen, it’s the females that go for blood – with mouthparts like miniature knives they slash through skin with a scissor-like motion. Clegs too are painful blood suckers. Greenbottles lay their eggs on a sheep’s dirty wool. When they hatch the maggots eat their way into the sheep’s flesh. This is known as ‘strike’. Large warble flies are parasitic with a most unpleasant life cycle. They lay their eggs on the forelegs of cattle and deer. When these hatch the larvae bore into the skin and migrate through the animal’s body until they reach its back growing bigger all the time. They show as lumps before the huge maggots pop out. Thankfully warbles were eradicated from the UK in 1990. Less damaging, but probably more stressful, are autumn flies which plague cattle and horses by gathering round their heads in large numbers. They breed in animal dung as do khaki coloured dung flies which feed on any insects attracted to cowpats. Another familiar fly is the Crane fly, better known as ‘Daddy Long Legs’, a large, flying, long-legged insect which, in late summer, can sometimes be disturbed in their thousands when walking across grassland. They themselves do not bite although their larvae, better known as leatherjackets, cause untold damage beneath the ground by eating plant roots. Frit flies can seriously damage cereals and other major crop pests are aphids, thrips, greenfly and carrot flies.

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