There are 16 native species, 4 of which are rare. Bats are very small nocturnal mammals. Britain’s most common bats, the two common pipistrelle species, measure only 3.5-5cm long and weigh just 3-7g, although their wingspan is comparatively large at 19-25cm. The other common garden and building dweller, the brown long-eared bat, has a slightly larger body (4-5cm), a weight of 5-12g, and a wingspan of 22-29cm. Other species can weigh up to 40g, measure between 3.5 and 8.2cm long and have a wingspan of 19-40cm. Browns and greys are typical bat liveries.

Bats, like so many wild animals, are under stress from human practices. In particular, there has been a loss of insect-rich feeding grounds such as permanent pasture, woodland, hedgerows and wetlands. Roofing timbers are often coated with toxic chemicals and rotten wood is often replaced with PVC. Many barns and roof spaces have been converted for human use. Bats are increasingly under threat from disturbance to their roosts, including tree cutting, the treatment of roofing timber with toxic preservatives and insecticides, and loft fumigation. Cats are a nuisance so block their entrance to roosts without blocking the bats.

It's not all doom and gloom, however. Humans have accidentally provided new feeding grounds such as over the lakes of disused quarries and open cast mines, canals, parkland, orchards, suburban gardens and urban areas, and the congregation of moths around street lamps also proves particularly attractive to them.

Bat boxes are ideal for making more places to roost, breed and hibernate. They are installed on a tree or wall. According to the Bat Conservation Trust, 11 bat species have roosted in bat boxes, 6 (pipistrelle, Natterer’s, noctule, Daubenton’s, Leisler’s and brown long-eared bats) have bred in them and they are often used as mating roosts.

Since bats are insectivorous, the key to attracting them is to provide habitats which encourage a rich insect population such as a pond, bog garden or meadow, or to plant old-fashioned cottage garden plants, night-scented plants e.g. evening primrose, wild flowers e.g. bladder campion and shrubs and trees e.g. honeysuckle. Herbs such as lemon balm, mint, marjoram and chives are also insect magnets.

Sheltered corners can be created that are warm and wind free such as between fences, walls, sheds and garages where insects will swarm in the evening. Leaving a lawn or part of it unmown from the middle of May is useful if it is not under a mowing regime for a wild flower meadow as insect larvae will thrive there. A low-powered night light will also attract insects. Do not use pesticides as poisoned insects will be eaten by bats.

A bat will usually fly in a 6-10km radius from the roost to feed, often on the same flight path or ‘beat’. The diet of British bats consists mostly of insects (they do not suck blood from animals in Britain). Depending on the species, they eat: midges, gnats, mosquitoes, flying ants, earwigs, lace wings, caddis flies and other flies, beetles, spiders, moths, caterpillars and ‘woodworm’.

Bats fly at night and navigate and find prey using echolocation. This involves emitting sounds that are usually way above the highest frequencies that humans can hear (25-115 kHz). The disproportionately large ears help in this process. Food is eaten on the wing or taken to a perch.

Gestation lasts 4-11 weeks depending on the species but usually 6-8 weeks. Usually one litter is produced each year. One or two young, occasionally twins, are born in summer into the mother’s wings while she hangs. They are minute and weigh only a few grams. They are blind and naked at first, open their eyes after about a week and can fly at 3-6 weeks. They are weaned from the mother’s milk to insects at 4 to 8 weeks.

Bats usually have different summer and winter roosts. In summer they need to be warm to be active whilst in winter they need a cold place for hibernation. They have historically roosted in tree holes, caves and rock fissures but have now colonised human spaces. Summer roosts include stable blocks, timbered barns, tunnels, mines, bridges, cellars, old stone buildings such as castles and churches, cavity walls, hedges, bat boxes and even oil rigs. Winter roosts are more difficult to assess because the bats are quiet and hidden away but they are known to include disused mines, disused chimneys, cellars and bat boxes. Hibernation lasts from early autumn until spring. They sometimes wake in warmer weather and leave in search of a better place to hibernate.

Some bats are solitary, such as noctule and serotine bats. Some, such as the brown long-eared bat, form small groups of 10 to 25. Others, such as the noctule, form roosting colonies of 25 to over 1000.

Enemies of the bat include domestic cats which climb into larger roosting spaces and natural climbing predators including rats, stoats and weasels and flying predators, especially owls, magpies and birds of prey.

Variable depending on the species. Some are very common, some under threat, endangered or sadly, extinct in these isles.

While some bats do not migrate or only locally, others migrate hundreds of kilometres. Echolocation and a bat’s flight are both very accurate so they do not get caught up in long hair. Another myth is that they are blind. Their eyesight is good, although it is not in colour. Bats live from 9 to 30 years depending on the species.

If a nest box becomes unsafe, perhaps because the wood has rotted, erect a new box nearby and allow time for the bats to move home before dismantling the old one (unless it is unsafe for people walking underneath). Ask a wildlife organisation for advice if you are unsure. It is illegal to disturb or obstruct a roost.

Don't believe people who tell you bats will suck your blood! British bats are insectivorous. If a bat ‘shows its teeth’ it is scanning you with its echolocation.

Up to 3000 small insects may be consumed in one feeding session.

Watch at dusk about 10 minutes to an hour after sunset as bats leave their roost to feed, often on a regular ‘beat’ very close to buildings. Tell-tale dry droppings (guano) will be present on the ground below a roost if the bats are in residence. The droppings are harmless in lofts (unless a massive weight builds up) and they are a good fertiliser - just cover any materials stored in the loft. Building work will not be prevented but advice from a local conservation trust is necessary to minimise harm. Do not handle bats.