Install a Bat House for Natural Pest Control
(Page 3 of 4)
September/October 1990
By the MOTHER EARTH NEWS Editorial Staff
Where are bat houses most likely to be needed?
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Bats are most likely to look for alternative roosts such as bat houses in areas where roosting places are insufficient to house as many bats as the local insect population can support. Examples of such places include areas where forestry practices have largely eliminated old hollow trees, or neighborhoods where bats have been excluded from attics or wall spaces. Conditions for your bat house don't have to be perfect for it to be occupied. Even natural roosts are seldom ideal.
Do bats migrate south for the winter, or will my bat house be used year round?
In Canada and the northern two-thirds of the U.S., all bats migrate south or find safe hibernating sites for winter. Very few species can long survive subfreezing temperatures. Tree-roosting species travel south, while those that would occupy bat houses generally move to an undisturbed cave or abandoned mine. The big brown bat is so exceptionally hardy that it sometimes overwinters in the outer walls of buildings. Bats might overwinter in bat houses only in southern or coastal areas where winters are mild.
If I put up several bat houses, will I attract more bats?
Europeans often put up four at a time around a tree trunk. They arrange them to face each direction, providing a variety of temperatures so as to better meet the bats' seasonal needs. In some cases, people who put up two or more houses at once report that all are occupied. In one case, however, one of two houses mounted side by side was used by 30 bats, while the other was ignored over a period of two years. Although it is difficult to anticipate how many bat houses might be needed in a given area, one might reasonably assume that more of them would attract snore bats. However, use of more than four is not recommended until at least one has been occupied, thereby confirming a local need.
How effective are bats at pest control? Do they really curb the mosquito population?
While birds, such as purple martins, play a major role in controlling day-flying insects, bats are by far the most effective checks against nightflying species, including such pests as mosquitoes, corn borers and cutworm moths. The amount a bat eats varies with season and stage of reproductive cycle, sometimes as much as tripling for nursing mothers. The actual number of insects caught varies, ranging from less than a hundred moths or beetles to thousands of smaller insects, such as mosquitoes, per night. In fact, bats probably require a mix of several kinds of insects, as the abundance of nightly and seasonal hatches varies.
Laboratory studies have demonstrated that a single little brown bat can catch up to 600 or more mosquitoes in an hour. This and other species have been documented in the wild as feeding heavily on several species of mosquitoes when they are available. A single endangered gray bat may catch 3,000 insects in a night, and large colonies can consume countless billions. The Mexican free-tailed bat colony in Texas's Bracken Cave, for example, catches nearly half a million pounds of insects nightly! It takes 20 million bats to do that, but even 30 little brown bats from one bat house easily could catch more than 30,000 insects in an evening's feeding. No control is perfect, but when it comes to reducing mosquitoes, no bug zapper is a match for bats.
