INHS Reports November-December 1999

The Naturalist's Apprentice: Build a House for Bats!

Bats can eat large numbers of night-flying insects, so many people are now realizing their benefits. Bats can be enticed to roost during the day and even rear their young in bat houses. A simple bat house can be constructed from the following plans. Bats like tight-fitting places, so even though the space looks crowded to you, it will not look that way to a bat. Bats prefer warm houses, so placement of the house is important. Position the house 15 to 20 feet high on an exposure that receives at least 6 hours of sunlight. Any exposure except north should be fine. The best sites are 20 to 25 feet from trees and other obstructions. Houses should be placed on the side of a building or on a pole, not in a tree. Put the bat house in place in April or May. It may take a year or more before the house is occupied. Bat houses within a quarter of a mile of water, such as a river, stream, or pond, are more likely to be successful in attracting bat residents.

Constructing the bat house (see diagram below)

* Cut the bat house pieces from 1 x 10 board using the dimensions shown in the diagrams. All surfaces shown with cross hatches should be roughened so the bats can grip them. If the surface is not already rough, brush it vigorously with a wire brush, or staple plastic window screening material to the smooth wood.

* Nail or screw the bat house together. Drilling small pilot holes for the nails or screws will help prevent the wood from splitting. Take special care when placing the center partition so that the spaces are 3/4 inch wide. It should also be placed about 1/2 inch from the top, fastened to the side panels only. The front ventilation hole should be about about 1/2 inch wide. All seams are caulked with latex caulk. All exterior surfaces, except for the landing stage, should be painted with at least two coats of exterior latex house paint of a dark color, preferably dark brown, gray, or green. The interior and the landing stage should be left unpainted.

* Screw or nail the bat house to the side of a building or pole.

Teachers or parents

Supplies needed: one 6-foot-long 1'' x 12'' board such as pine or rough-surface cedar (rough-surface cedar will have one side that is already rough enough for a bat to grip); 30 1 1/4''-long nails or screws; latex caulk; dark-colored latex paint.

Tools needed: wire brush, hammer or screwdriver, paint brushes, drill with bit slightly smaller than the diameter of the nails or screws.

Cut the wood pieces out for younger children, or have a shop class cut them out. The upper front panel and the roof must be cut at a 45-degree angle. Plywood can be used instead of cedar or pine, but if it is of a different thickness (1'' lumber is actually about 3/4'' thick), you will have to adjust the size of the side panel and roof. Different species of bats prefer different spaces for roosting, but this bat house is a good compromise for most. Spaces between partitions can be as small as 1/2 inch for some species, and as large as 1 inch for others.

Please remind everyone not to touch the bats.

Carolyn Nixon, INHS Office of the Chief

If you get bats in your bat house, let us know! (e-mail or write.....)

c-nixon2@uiuc.edu
Carolyn Nixon
Illinois Natural History Survey
607 E. Peabody Dr.
Champaign, IL 61820

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