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There are 19 families of bats throughout the world but only 2 families are represented in Britain, the Vesper bats and the Horseshoe bats.
Horseshoe bats
Two species occur in Britain, the greater horseshoe and the lesser horseshoe. They owe their name to the horseshoe shaped nose-leaf which helps modify and direct the ultrasonic sounds emitted through the nostrils. They hang from the roof with wings folded around themselves. The rapid decline of horseshoe bats is not fully understood, though certainly many large nursery colonies have been destroyed, accidentally and deliberately. Both species are very dependent on caves and cave-like structures with high humidity for roosting, especially in winter, but they also use old houses in summer.
Greater Horseshoe bat (Rhinolophus ferrumequinum)
This is one of our most endangered bats, now restricted to the south-west of England and southern Wales. It has a wingspan of about 39cm with a slow fluttering flight and needs an ample supply of large insects.
Lesser Horseshoe bat (Rhinolophus hipposideros)
This bat also occurs further north and west and in western Ireland. With a wingspan of only 25cm it has a faster and more twisting pattern of flight than the greater horseshoe. Craneflies are an important part of its preferred diet.
Vesper Bats
This family all have simple dog-like noses and shout through open mouths when echolocating. Each species has a different shape of wings and ears and its own preferred prey and method of feeding. They fold their wings at their sides when at rest and are able to crawl, often creeping into crevices to roost. Below are notes on four of the species most likely to be seen.
Pipistrelle bat (Pipistrellus pipistrellus)
This is our smallest and most common bat throughout Britain. With head and body only about 3.5cm long and wingspan about 22cm, it will fit comfortably into a matchbox with wings folded. Flight is fast and erratic and it may often be seen patrolling a regular 'beat'. Over 3,000 tiny insects, such as midges and mosquitoes, may be eaten when insects are plentiful. Modern houses are popular for nursery roost sites, between the roof tiles and underfelt, behind barge boarding or in other confined spaces.
Brown Long-eared bat (Plecotus auritus)
The brown long-eared bat is found all over Britain, especially near trees and wooded areas. It has a wingspan of about 25cm with broad wings that make it very manoeuvrable as it flies in and out of the foliage of large trees, sometimes hovering before plucking moths from the leaves. It is easily recognized by its exceptionally large ears.
Daubenton's bat (Myotis daubentoni)
Once known as the water bat, this medium-sized bat is found in most parts of Britain. With a wingspan of about 25cm, it skims over lakes and rivers in a swallow-like flight, taking insects from close to the surface of the water.
Noctule (Nyctalus noctula)
The noctule is one of our largest bats with a wingspan of about 36cm. It is not found in Ireland. It flies very high, swooping onto large insects which it eats in flight. Only rarely found in houses it is very dependent on trees for roosting, both in summer and winter.
Information supplied by The Bat Conservation Trust