This large dark specie, the size of half a hand, usually roosts in houses or in hot church attics. Ears and muzzle are black, the fur is dark smokey brown. Despite of its impressive size, it's a shy bat that quickly disappeares between beams or hollow walls. Near Bourges, 40 colonies are monitored by the museum. Along with the pipitrelle, it's one of the most common bats of the area. Colonies usually gather from 30 to 100 females. Serotines leave their roost just after dusk, crawling between roof tiles or cracks.