Ghosts,
goblins, and bats are some of the scary creatures found on Halloween night. The
insectivorous bats of the Midwest, however, are the good guys on any other
night. These nocturnal hunters have an undeserved bad reputation, and their
contributions to natural control of mosquitoes and other insects is often
overlooked.
Bats are the only true flying mammal. Worldwide there are as many as 1,000 species. Wisconsin has eight species of bats, five of which spend winters here, hibernating in caves, shafts, crevices and buildings. The Midwestern species most commonly found roosting in houses are the big brown (Eptesicus fuscus) and the little brown bat (Myotis lucifugus). In some circumstances – such as when their droppings, noise, intrusion, odor, mites, or lice become a nuisance – control is necessary. But because of their beneficial value, bats should be appreciated and not needlessly killed.
The specific impact of bats on insect populations has not been studied, except in very general terms, but it has been documented that a single bat can catch and eat 500 or more insects in an hour. Most bats eat from ¼ to ½ their body weight in insects nightly at such a feeding rate that an average-sized bat will consume 4 to 8 pounds of bugs in one year! They also consume many other pests, such moth and beetle agricultural pests, and other nuisance pests, but some of the arthropods consumed by bats may be beneficial as well. They are often attracted to insects flying around swimming pools, ponds or white lights.
Bats
locate prey and avoid obstacles by using ultrasound, or high frequency sounds.
They also emit audible sounds to communicate with each other. They usually leave
their roosts to feed between ½ hour before and ½ hour after sunset, usually on
calm days. They often return during the night to rest before leaving to forage
again until dawn and return to sleep during the day. Around the time of the
first frost, bats prepare for the winter hibernation.
In general, most species of bats mate in fall and winter. Pregnant females leave their hibernation sites and congregate in maternity colonies to give birth between May and July. Usually they have one offspring. Young bats are able to fly within 3 weeks and when they are weaned in July and August, the nursery colonies disperse.
Earlier in the 20th century bat roosts were built to try to concentrate bats in particular areas in order to use them to control insects. The first "malaria eradication guano-producing bat roost", built in 1911, targeted malaria-transmitting mosquitoes in Florida. Most bat houses these days are erected for conservation purposes, since many species of bats are now threatened. One of the most important factors in the decline of bat populations in the United States is the destruction of natural roosts either directly or indirectly by human activities.
Artificial
roosts are common in Europe where bats have been protected for over 60 years.
Europeans have bat houses much the same way we have Purple Martin houses
in the Midwest. It appears that bat houses may attract
bats that are displaced from a structure. Bat houses should be located away from
human high use areas, and not near bright lights. They can be placed on a
barn, pole, or the side of a wooden building, but needs to be in place by early
April. Mounting two bat houses back to back on
poles is ideal (face one house north, the other south). Bat houses should always
be mounted at least 12 feet above ground, although 15 to 20 feet is better.
The best habitat for bats is within a half mile of a stream, lake or
wetland. It can take up to two years for a bat colony to find your bat house.
Make sure your bat house is constructed and positioned properly. Short stout houses tend to have little chance of attracting bats; longer, wider houses typically have up to an 80% occupancy rate. Bats also need high temperatures to thrive. The optimum internal bat house temperature for maternity colonies in summer is between 80º F to 100º F as long as possible, so place the bat house where it will receive direct sunlight. In our area, at least six hours of direct daily sun is recommended. Dark paint on the exterior of the bat house will also help.
You shouldn't be afraid of bats living nearby. Bats in our area do not suck blood and they won't fly into your hair. Although rabies can be carried by bats (or any wild, warm-blooded animal), only of 1% of all bats actually have rabies, which is about similar for any other wild animal.
– Susan Mahr, University of Wisconsin
