Etymology

 

 Appearance

Fur: Glossy, yellowish to dark brown above; paler below; hair-basal half contrasting light tip.

Tail membrane: Dark brown, mostly naked.

 Wing membrane: Dark brown, mostly naked except scattered hairs and basal fur.

 Calcar: None or slightly keeled.

 Ears: Small «16 mm), do not extend 2 mm beyond nostrils when laid forward; dark brown and naked; narrow with bluntly rounded tip.

 Tragus: About one-half ear length; blunt tip; not obviously curved.

 Other: Toe hairs long, extend beyond claw. Total length: 76-95 mm.

 Forearm: 34-41 mm.

 Wingspan: 222-269 mm.

 Total weight: 6-9.5 g.

 Tooth number and formula: 38 total; I 2/3; C 1/1; P 3/3; M 3/3.

 Confusing Species

 Indiana myotis (M. sodalis): Toe hairs do not extend beyond claws; keeled calcar.

 Northern myotis (M. septentrionalis): Ears long (16 mm), extend at least 2 mm beyond nose when laid forward; tragus longer and pointed.

 Big brown bat (E. fuscus): Larger size (>10 g) and longer forearm (>42 mm); tragus clearly less than one-half ear length.

 Distribution and Status

 Overall: Most of North America except southern Great Plains to central Mexico.

 Iowa: Statewide in summer; most common in eastern half. In winter, most migrate southward; some hibernate in eastern Iowa caves and mines.

Greek: mys-"mouse"; ous -"ears." Myotis refers to the resemblance of some bats' ears to those of mice.

 Latin: lux-"light" and fugilo - "to flee"; lucifugus refers to the nocturnal habits of bats.

 Natural History

 The little brown myotis is one of Iowa's most common bats, frequently using man-made structures in summer, but not in winter. As a house bat, this species, along with the big brown bat, may be encountered by humans thus making it a frequent target of control efforts.

 In summer, females establish nursery colonies of up to 1,000 adults in either man-made structures such as buildings, bridges, culverts, and mines; or natural cavities, including hollow trees, under loose bark, and cliff crevices. Males and barren females usually roost singly or in small clusters in similar places but away from nurseries.

 The little brown myotis emerges from summer roosts at dusk to feed. Foraging by individuals often begins over water, along forest edges or in clearings, but the pattern varies considerably and may include group foraging. Although aquatic insects form a significant part of the diet, stomach and fecal analyses show preference for moths, leafhoppers, plant-hoppers, beetles, wasps, flies, mosquitoes and midges.

 Mating takes place in the fall with females storing sperm until spring when fertilization takes place. Since the actual time of fertilization varies with environmental conditions, birth of the single young varies accordingly. In Iowa, young are born in the nursery colonies from early June to early July and are capable of flight about three weeks after birth. After the nurseries have disbanded in late summer, males frequently join the females as migration begins. In the fall, little brown bats often form swarms in caves or mines. At that time, large numbers may be seen over the Mississippi River.

 In winter, both sexes hibernate in eastern Iowa caves and mines, but not buildings. The little brown myotis often hibernates near other species, including the big brown bat, northern myotis, and eastern pipistrelle. Hibernacula are usually above freezing and roost sites relatively humid. Many individuals that spend the summer in Iowa migrate southward to similar hibernacula.

Because little brown bats are frequent summer house residents, many people assume their populations are not declining. While such assumptions may be valid where adequate habitat exists, populations may be limited by availability of summer nursery sites. The recent demise of many man-made roost sites (e.g., wooden barns, churches and bridges), coupled with general forest and roost tree loss, may account for apparent localization of the species in parts of Iowa, especially central and western counties. However, the little brown myotis still appears to be widespread and common in eastern counties.