The gray myotis, or gray bat, is the largest of all Missouri’s myotis (or mouse-eared) bats (genus Myotis). It is an endangered species.
Although the different myotises can be difficult to distinguish from each other, gray myotises are easy to ID if you know what to look for.
Gray myotises have gray fur that is a uniform brownish gray most of the year, turning a light rusty brown in summer. Other myotises have bi- or tricolored fur, with the tips of each strand contrasting with the base.
The gray myotis’s ears and wing membranes are gray to black. Often, there is an orangish patch under the ears and chin.
During hibernation, gray bats form large colonies, typically in caves, that can comprise hundreds of thousands of bats. Unlike Indiana bats, which also form large colonies, the clusters of gray bats appear chaotic and loosely packed, with individual bats hanging off of each other and their forearms extending to cling with their thumbs as well as their feet.
In addition to the characters described above, specialists confirm identifications with the following:
- There is a distinct notch on the inside curve of each claw.
- The wings attach to the ankle and not at the base of the toes (note that the southeastern myotis can also have wings attaching at the ankle).
For your safety and the safety of bats, do not handle bats. Biologists who study bats receive special training and pre-exposure rabies vaccinations. Bats are not aggressive toward people but will bite in self-defense if handled. If you absolutely must handle a bat, wear heavy leather gloves. For more information about bats, see the bats group page.
Similar species: Missouri has five other species of bats in genus Myotis:
- Southeastern myotis (M. austroriparius)
- Eastern small-footed myotis (M. leibii)
- Little brown myotis (M. lucifugus)
- Northern long-eared myotis (M. septentrionalis)
- Indiana myotis (M. sodalis)
For more information about Missouri’s bats as a group, visit the Bats page.
Total length: 79–95 mm (3⅛–3¾ inches); tail length: 31–44 mm (1¼–1¾ inches); weight: 7–15 g (about 0.25–0.5 ounce); forearm length: 40–47 mm (about 1½–1⅞ inches); wingspan: 27–30 cm (about 10½–11¾ inches).
Missouri contains about 20 percent of the total population of gray myotises. Most of the known gray myotis caves are south of the Missouri River, particularly in the Ozarks, although a few exist north of the river.
Habitat and Conservation
This species once flourished in limestone caves, especially caves within two miles of rivers, streams, or lakes.
Conservation efforts include protecting known gray myotis wintering and nursery caves from disturbance, reducing the use of pesticides (which not only affect their prey but also accumulate in the bat's tissues and mother's milk), and maintaining wooded corridors along streams. White-nose syndrome, a deadly fungal disease, is a new and grave threat to this species' survival.
Gray bats rely very heavily on a relatively small number of caves, with some caves hosting tens or hundreds of thousands of these bats. They are also very sensitive to disturbance; even just walking around a cave quietly with lights on may cause them to take flight, potentially dislodging pups or interrupting hibernation.
Although still listed as endangered, this species is recovering well due to protection of such sites. Gray bats may one day be eligible for downlisting or delisting from federal and state endangered species lists, assuming we continue to protect the caves they rely on.
Food
Gray bats typically forage over water for insects, including caddisflies, moths, stoneflies, mayflies, flying beetles, true flies, and moths. The Asiatic oak weevil is a favorite summertime food, when it is abundant in forested cliffs along rivers. Most insects are eaten on the wing.
Status
Listed as endangered by both the Missouri Department of Conservation and the U.S. Fish and Wildlife Service.
Recovery efforts have been showing signs of success, and this species may one day be eligible for downlisting to "threatened," or delisting entirely.
Life Cycle
Pregnant females roost in maternity colonies in caves separate from males and young females from late May to June. These are different caves than the ones they use for hibernation.
In winter, gray bats prefer cold air trap caves, but in the summer, the mothers need warm air traps in order to raise their young.
Each female gives birth to a single young in June. The young are able to fly 4 weeks later. Mothers and young rejoin the bachelor colonies in July and August.
Gray myotises exhibit great loyalty to their roosting and hibernating sites and will return to the same caves year after year.
Control
Human Connections
Bats eats untold numbers of flying insects.
It is important for people to stay out of nursery caves: If disturbed, pregnant females may abort their young and babies may drop from the wall to the floor or stream below and die. A single disturbance can wreck a colony’s reproduction for the year.
Ecosystem Connections
Bats help control populations of flying insects.
Their presence in caves is a crucial part of those unique underground ecosystems. By collecting organic material (insects) from outside the cave and bringing it in (as guano), bats help provide the basis for a variety of cave life forms.
