Can Bats Control Mosquitoes?

   With all of the recent precipitation received, many people are seeing an increase in the mosquito population. 

Some people have asked if building and installing “Bat Houses” will help control their mosquito population.

So, can bats control mosquitoes?

With nearly one thousand species, bats dwell in most places on earth, except for extremely cold or hot climates and some remote islands. In the United States, 45 species have been recorded, of which 22 have been found in Nevada. While many species of bats reside in caves or mines, others inhabit trees, old buildings, bridges or culverts. Bat houses can provide shelter for bats in suburban areas.

Most species of bats feed on a wide variety of insects. The three orders of insects most commonly consumed by bats in the United States are moths (Lepidoptera), beetles (Coleoptera), and flies (Diptera). 

Although many bats eat insects in the family that contains mosquitoes (Diptera), most bats don't seem to have a strong liking for mosquitoes.

Research conducted in the 1950’s indicated that bats released in a room filled with mosquitoes could catch up to 10 mosquitoes per minute. The research was conducted to measure the effectiveness of echolocation in insectivorous bat species. 

The results have been extrapolated to suggest that wild bats can consume 600 mosquitoes per hour. Using that figure, a colony of 500 bats will remove 250,000 mosquitoes each hour and theoretically afford mosquito control for an entire neighborhood.

Research since that time has shown that insectivorous bats are opportunistic feeders and that mosquitoes make up a very small percentage of their natural diet. Bats’ behavior when locked in a room with nothing to feed upon but mosquitoes has no bearing on their behavior in the wild. Bats feed on the same insects that turn up in bug zappers and are no more effective for controlling mosquitoes than their electronic equivalent. Providing habitat to enhance bat populations is an admirable activity for conservation purposes. Using mosquito control as the reason to initiate public interest is misleading at best.

Therefore, given the small quantities of mosquitoes consumed by most bats, it is unlikely that bats would be effective at controlling large mosquito populations. 

However, large colonies of bats will certainly reduce the number of insects nearby. Bats are beneficial for insect control not only because they consume large quantities of insects, but because many insects avoid areas where they hear bat calls. 

Therefore, attracting bats to an area where a natural form of insect control is desired can be a smart idea.

What Can You Do to Attract Bats?

Bats roost in both naturally occurring and man-made structures. Natural structures used by bats include caves, rock crevices, hollows inside live and dead trees. Man-made structures used by roosting bats include mines, bridges, culverts, buildings, and specially made bat houses. These areas should be left undisturbed if you want to attract bats.

Research conducted by Bat Conservation International (http://www.batcon.org) has determined bat house characteristics that bats find most attractive. Bat houses with chambers at least 14 inches wide and at least two feet tall have a greater chance of attracting bats than narrower or shorter houses. 

A landing area beneath the entrance at least three inches long with a rough surface for bats to grab onto when they fly to the house is critical for facilitating access. If a bat house has only one chamber for bats to roost in, roughen the entire back panel of the interior of the house so that bats can easily grab onto the surface with their toes. If the house has more than one roosting chamber, roughen at least one side of each of the partitions separating the chambers.

The color of the exterior of a bat house is an important consideration because it influences the temperature inside the house, and bats select roost sites according to interior temperatures. After you caulk all the seams, paint your bat house with three coats of flat, exterior-grade, water-based paint or stain to increase its lifespan. 

Two characteristics of the location where the house will be mounted influence which paint color would be best: the temperature and the number of hours of direct sun exposure. A house located in a spot that receives direct sunlight for only a few hours each day should be painted a dark brown or dark gray, whereas a light brown or gray would be more appropriate for a site with a lot of sun. Darker colors absorb heat from the sun, whereas lighter colors reflect heat from the sun.

Bats prefer houses that do not allow rainwater to seep in. Careful caulking of all seams (with latex caulk) can prevent leaks. Re-caulk every three to five years during a time of year when bats are not present. Some houses may be used continuously by bats for long periods each year, whereas other houses may receive intermittent use throughout the year. 

To determine a time of year when bats are not using the house, shine a flashlight or spotlight up into the house from below during daylight hours and check for occupants. Do not take the house down for recaulking when bats are present.

Although it is important that houses are watertight, bat houses should not be airtight, due to warm temperatures. A single, ½-inch-wide vent placed horizontally along the entire front of the house about 6 inches from the bottom can promote airflow. Vents 6 inches tall and ½ inch wide on the side of the rear chamber can also increase air circulation. Shingles or sheet metal over the roof can increase longevity of the house. 

A roof that provides a wide overhang will provide some shade during the middle of the day, reducing the chance that bats could overheat.

Bat houses can be put up any time of year. However, bats are most likely to move in during the early spring, so it is best to put up houses during the winter so they are available when bats are actively searching for roosts. If bats are being excluded from a building and bat houses are being provided as alternative roost sites, they should be put up several weeks before the eviction.

Bat houses located on the sides of buildings or on poles are more likely to attract bats than bat houses mounted on trees. This is because houses on trees tend to be shaded by foliage and tend to provide perch sites for predators, both of which are bad for the bats. 

Poles and buildings are better alternatives because they offer more exposure to sunlight and fewer perch sites for potential predators such as owls, hawks, and falcons. Bat houses should be located at least 20 feet from potential perch sites for predators and at least 12 feet off the ground.

If mounted on a metal or wooden pole, a conical piece of flashing wrapped around the pole can prevent potential predators (such as snakes) from climbing the pole.

Small bat houses are relatively simple to build and the materials required are fairly inexpensive for information on how to build a bat house go to: (http://edis.ifas.ufl.edu/UW290 – “Effective Bat Houses for FL” EDIS). Manufactured bat houses are available at many stores and also online. However, many pre-made houses will not attract bats because of poor design or construction.

Source: Effective Bat Houses for Florida, Holly K. Ober, University of Florida Extension.