The pipistrelle is the smallest and most common of Britain's 18 species of bat. It belongs to the Vespertilionidae family of bats, known as ordinary or earlet bats, and appears earlier in the evening than most other bats. It has a jerky, erratic flight, flickering its wings rapidly as it pursues its prey.
The jerky flight of the pipistrelle gave rise to the ancient name for bats - flittermouse (Fledermaus in German.)