Natterer’s bats are a medium-sized member of the Myotis family of bats. They can be distinguished from the other members of the family by their narrow, pointed ears that slightly curve towards the end. They also have a characteristic red colour to their limbs, which give rise to its name, the ‘red-armed bat’.
Head & body length: 40mm – 50mm
Forearm length: 36mm – 43mm
Wingspan: 245mm – 300mm
Weight: 7g – 12g
Colour: Fur light buff brown on black, white underneath. Bare pink face.
Natterer’s bats are often found amongst woodland, where their relatively short, broad wings make them highly manoeuvrable at slow speed. With their ability to fly slowly and hover, they often take prey from foliage, including flightless invertebrates, such as spiders, or day-flying insects that are roosting on the leaves and branches.
Natterer’s bats are most often found roosting in old stone buildings with large timber beams, such as barns, large houses and churches. They often roost in small crevices in or around the wooden beams. They can also be found roosting in trees, in knot holes or damage features. They are generally late to emerge from their roost, being about one hour after sunset. They are known to change roost sites frequently.
Natterer’s bats often hibernate in cool caves and mines. In Cumbria, we often find them hibernating in the limestone caves near Kirkby Lonsdale, but can also be found in stone crevices, such as in culverts and bridges.
They eat mostly flies (mainly midges), small moths, caddis flies, lacewings, beetles, small wasps, and spiders.
Natterer’s bats have very quiet echolocation calls. The frequency of their calls range from 80 kHz down to 30 kHz, a very wide range of frequencies. When heard on a bat detector, their calls are heard as irregular rapid clicks.
Although Natterer’s bats are found throughout the UK, they are generally uncommon. As they often roost in large stone buildings, they are regularly found in Cumbria. The UK population of Natterer’s bats is of international importance.