It’s rather lovely sitting out on a mild evening and seeing bats zipping about in the fading light. I’m always happy to see bats over the garden, hunting for dinner. If they’ve found plenty of insect life it’s a good sign of a thriving eco-system.

As far as I know, the only bats I’ve seen are pipistrelles, the UK’s most common bat. There are, however, 18 species of bat in the UK, which amounts to almost a quarter of our resident mammal species.

I remember going to a local event about bats when I was a child. We were asked to show with our hands how big we thought a pipistrelle bat was. Children waved their arms wildly in the air, demonstrating the size of these apparently enormous creatures. The expert explained that my hands, about 20cm apart, were about as wide as the bats’ wingspan.

In contrast to the giant suggestions from around the room, a pipistrelle’s head and body together are less than 5cm long, and they weigh no more than a pound coin. Even our largest bat, the noctule, is still small enough to fit in the palm of your hand.

A single bat can eat up to 3,000 insects in one night

Common pipistrelles emerge around 20 minutes after sunset over the milder months. They can fly at seven metres per second as they hunt and dive for prey in flight. Using echo-location, a single bat can catch and eat up to 3,000 insects in one night. They eat mostly small flies, including mosquitos and midges which emerge from water.

If you have a garden pond (or even a bucket of water sitting around for a while!) you may have seen that wiggly mosquito larvae are one of the first things to inhabit the water, and they attract lots of creatures that will eat them. Bats are no different. On a warm summer’s evening you may well see them over ponds, collecting the mosquitos which are attracted to the water or emerging as adults from the larvae.

At this time of year, pipistrelles and other bats will be becoming less active as the temperature cools. They will be in full hibernation by December and reappear again in the spring.

Interestingly, pipistrelles mate in the autumn, but fertilisation doesn’t occur until after hibernation. Females are pregnant in May and June, and then usually have a single pup which is raised in a maternity colony with many other females and young.

Bats like to hibernate in buildings where they can take advantage of warmth and shelter. You may have one or two settling down in your roof, behind tiles or soffits, under eaves or in other small crevices. If so, lucky you.