Description: This is one of the smallest bats in Kansas, and can be distinguished from other Kansas bats by: 1) a total of 34 teeth, 2) yellowish-brown fur on upper parts with lighter underparts, 3) individual hairs dark at the base and tip with a wide light middle band, 4) reddish skin of the forearm contrasting with black wing membrane, 5) the short, blunt tragus which is less than one half the length of the ear, and 6) the ear, which is noticeably longer than wide Sebaceous skin glands on the upper lip and throat produce a distinctive odor. Sexes are alike and there is no seasonal change in color of hair. Young are darker than adults.
Size: Adults may attain the following dimensions: total length 75-90 mm; tail 33-43 mm; hind foot 8-11 mm; ear 12-14 mm; weight 4.5-8 grams.
Range and Habitat: The eastern pipistrelle inhabits the eastern half of Kansas, extending farther west in the southern part of the state. In summer it is found roosting in rocky areas, in buildings, and in trees. When inhabiting caves, it is generally in the exposed parts of the entrances where there is light. In winter it hibernates deep in caves, sinks or mines where it is associated with the most suitable and stable conditions of relatively warm temperature and high humidity.
Reproduction: Mating is in autumn and females carry sperm in their uteri until ovulation in spring when eggs are fertilized, either by the sperm already present in the uterus or by additional breeding in spring. In June or mid-July, two young (occasionally a single or even three) are born. In about three weeks the young are capable of flight and soon forage for themselves.
Habits: This is a relatively unsocial bat. When hibernating in caves, it is generally alone or in small loosely associated clusters, hanging upside down with the curved claws of its hind feet anchored onto the rough surface of the ceiling or wall. In adjacent states to the east the eastern pipistrelle enters caves in mid-October, the sexes in equal numbers. Both sexes use the caves until the end of April, but in mid-March start to leave. By mid-May only males are present, the females having left the cave to set up maternity sites. In summer both sexes live outside caves except for an occasional individual using the outer entrance for daytime roosting. This bat is generally nonmigratory although capable of moving 60 to 80 kilometers from its hibernating cave. Most of these bats, however, remain near their winter caves. The flight is weak and erratic, and is characterized by a fluttering motion.
Food: Food consists of small insects that are active in the evening and night. They are captured during two or three foraging intervals during the night. Hunting flights by this bat are often close to bodies of water, over open woodlands or along forest borders. Rarely do they hunt in dense forest or over open fields.
Remarks: Longevity of this species is known to be ten to fifteen years.