The western pipistrelle, Pipistrellus hesperus, is an exceedingly small bat found throughout Utah in deserts and rocky habitats, often near water. The species also occurs throughout many of the other western states and Mexico. Western pipistrelles roost in caves, mines, rock crevices, and buildings, usually singly or in small groups.
The western pipistrelle eats small swarming insects. Although most bats are nocturnal, the western pipistrelle usually feeds in the late evening and early morning, resting during the night. Young of the species are born in June or July, and the average litter size is two. Young learn to fly in about one month. Western pipistrelles are known to hibernate during cold weather, but individuals do become sporadically active during the winter months.