A Minnesota Homeowner’s Guide on Bats and Bat Problems

No other mammals in the Northeast are as misunderstood as bats. A variety of myths and misconceptions surround these small, nocturnal, flying mammals. Many people think of bats as vicious animals that carry diseases and get tangled in hair. Others consider them to be friendly, cuddly animals that need only our love and understanding. Both images are somewhat misguided. The reality behind the most commonly held misconceptions surrounding these beneficial mammals.

Benefits of Bats

Bats make good neighbors. As the only major preda­tors of night flying insects, bats play an important role in controlling many insect pests. A single bat can consume as many as 500 insects in just one hour, or nearly 3,000 insects every night. A colony of just 100 little brown bats, the most abundant species in the Northeast, may consume more than a quarter of a million mosquitoes and other small insects each night.

Big Brown Bat

Big brown bats, which live primarily in agricul­tural areas, feed on June bugs, cucumber beetles, green and brown stinkbugs, and leafhoppers. Research has shown that over the course of a sum­mer, a colony of 150 big brown bats can eat 38,000 cucumber beetles, 16,000 June bugs, 19,000 stink­bugs, and 50,000 leafhoppers and can prevent the hatching of 18 million corn rootworms by devouring the adult beetles.

The red, hoary, and silver-haired bats help to maintain forest health in the region by feeding on forest pests such as tent caterpillar


moths. Because of their role in controlling insect numbers through­out the Northeast and elsewhere in the United States, the maintenance of wild bat populations is important for maintaining ecosystem health.

Bat Behavior

Because few flying insects are active during the winter months, bats that remain in the Northeast year-round gather in caves and abandoned mines to hibernate. Hibernation is a state of prolonged torpor during which bats greatly reduce their normal metabolic activities. Body temperature in hibernat­ing bats falls from a normal level of more than 100o F to that of the surrounding cave temperature, usually 40–50o F. The heart rate slows to only about twenty beats per minute, as compared to 1,000 beats per minute during flight. By allowing their bodily processes to slow this way, hibernating bats can survive on a very small amount of stored fat during the five- to six-month hibernation period, losing from one-fourth to one-half of their prehibernation weight.

Bats arouse from hibernation during March and usually arrive at their summer roosts in April. At this time, pregnant females seek out sheltered roosts in rock crevices, tree cavities, and tree foliage in which to rear their pups. Female red, hoary, and silver-haired bats roost alone during the summer, while females of other species gather into large or small groupings called maternity colonies. Male bats usually roost alone in fairly exposed locations.

Depending upon the species, females give birth to one to three pups in late May and early June. The pups, which are born hairless, blind, and helpless, cling tightly to their mother in the maternity roost. On summer evenings, females leave the pups in the roost and hunt insects nearby, returning often throughout the night to nurse their offspring. As the pups grow older, the females return less frequently during the night. The pups begin to fly and hunt on their own by mid-July, when they are approximately five weeks old. However, the pups will continue to nurse until they can adequately feed themselves.

Maternity colonies begin to disband in late sum­mer and early fall. At this time, males and females of hibernating species begin to swarm together. Large groups of these bats will swarm in and out of cave entrances throughout the night, often roosting in the caves during the day. This swarming behavior brings adults together for mating, and may also teach young bats the location of the hibernation caves. Autumn also prompts the silver-haired, red, and hoary bats to begin their migration to warmer climates.

A Single Bat in the House

Individual bats occasionally enter houses, most of­ten during summer evenings in mid-July and August. These wayward bats are usually pups that are just beginning to fly. Fortunately, these incidents can be dealt with quite easily. A bat flying in the house will usually circle a room several times in search of an exit. The best method for getting a bat out of the house is to allow it to find its own way out. Chas­ing or swatting at the bat will cause it to panic and fly erratically around the room, which needlessly prolongs the incident.

If you do encounter a bat flying in a room, fol­low this procedure:

  1. Shut all doors leading into other rooms to con­fine the bat to as small an area as possible.
  2. Open all windows and doors leading outside to give the bat a chance to escape. (Don’t worry about other bats flying in from the outside.)
  3. Remove pets from the room, leave the lights on, stand quietly against a wall or door, and watch the bat until it leaves.
  4. Do not try to herd the bat toward a window. Just allow it to calmly get its bearings, and don’t worry about it swooping at you. When indoors, a bat makes steep, banking turns, so it flies up­wards as it approaches a wall and swoops lower near the center of the room.
  5. Within ten to fifteen minutes the bat should settle down, locate the open door or window, and fly out of the room.

If the bat tires and comes to rest on a curtain or wall, you can easily remove it without directly touching it. Follow the steps below, and remember to never handle a bat, or any other wild animal, with your bare hands.

  1. Put on a pair of leather gardening or work gloves.
  2. Place a container, such as a large plastic bowl,
  3. You can easily remove a bat from a room without directly touching it over the bat as it rests on the wall. At this point, the bat is probably exhausted and disoriented, and will not fly as you approach it. (If it does take flight, follow the procedure for flying bats.)
  4. Slide a piece of rigid cardboard between the container and the wall to trap the bat. Hold the cardboard firmly against the container and carry the container outside.
  5. Place the container (facing away from you) on a secure place above the ground—such as on a ledge, or against a tree—and slide away the cardboard. The bat will not fly right away, so releasing it above the ground keeps it safe from predators until it has its bearings. And unlike birds, most bats must drop from a perch and catch air under their wings before they can fly.


Bat-proofing a building involves sealing the bats’ en­trance holes and then providing the maternity colo­ny with an alternate roost, or bat box. Bat-proofing a building is usually a simple procedure that does not require the skills of a professional or any expensive materials. To bat-proof your home: (1) stage a “bat watch” to identify bat entrances, (2) seal the holes to prevent their entry, (3) provide an alternative roost, or bat box, for the colony to occupy.

If You Are Housing a Bat Colony

One way to tell if you are sharing your house with a bat colony is to simply go into the attic and look for roosting bats. During the day, bats will likely be roosting in narrow crevices in the attic walls, be­tween the rafters, or tucked into the space between the rafters and roofing material. When you enter the attic, the bats will quickly retreat out of sight (rather than taking flight). If you can’t see them, listen for the squeaking or scurrying sounds that will verify their presence.

If you are uncomfortable entering the attic when bats may be present, you can inspect the attic at night for bat droppings. The dry, black droppings are about the size of a grain of rice, and accumulate in piles below areas where the bats roost. (Mouse drop­pings look similar, but you would find them scattered in small amounts throughout the attic.) If you find bats living in your attic during the day, or if you find large accumulations of bat droppings, then you probably have a maternity colony in your house.

If you have recurring bat  problem entering your home, you may want to inspect your attic to determine if you are housing a bat maternity colony. Extreme care should be taken when attempting to catch a bat(s) if your home is currently under attack by bats it is wise to call a professional or if you need assistance in repairing the home damage  a Minnesota Wild Animal Management had experience in handling bat removals. Hiring a professional will guarantee the safety of you and your family along with preventing these bats from returning.


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