The two roosting chambers protrude from the outer shell.
Without the outer shell, you can see the spacers and inner shell boards
Assemble four outer-shell boards into a hollow, square box. Vent slots are on opposing sides and oriented towards the bottom.
Why does your small farm, homestead or backyard need bats? Because they’re Mother Nature’s natural, organic solution to insect and bug control. Cucumber beetles, June beetles, stinkbugs, leafhoppers, cutworm moths and corn moths—pests well known to farmers and gardeners alike—are among bats’ favorite food. Rice farmers in Spain, in fact, were able to completely eliminate the use of pesticides after they built a bat box and recruited a mere five bats per acre to their farm. According to estimates from the University of Pretoria, U.S. Geological Survey (USGS), University of Tennessee and Boston University, bats save agriculture up to $53 billion a year in crop protection.
“Bats can eat up to their own body weight in insects a night,” said Micaela Jemison, Director of Communication & Public Engagement at Bat Conservation International.
Bat Box Design
The two-chamber rocket box gives these helpful insect-eaters a home. And unlike other designs, it mimics the way bats naturally move within hollowed-out trees as the weather changes—from a sunlight side into the shade, or away from a cooling west wind.
“This is important as the seasons change, as the bats will be seeking warmer or cooler areas of the box to maintain their body temperature,” Jemison said. “Other bat house designs don’t necessarily give them this flexibility in temperature.”
Invented in the mid-1990s by former U.S. Forest Service biologists Dan Dourson and John MacGregor, the rocket box, so-called because of it’s shape, is now being successfully used around the country with at least eight species of bats. A pole-mounted bat box is essentially two 3-foot rectangular wooden shells that fit over each other creating two narrow bat-nesting chambers. The long continuous chambers let bats move to warmer or cooler spots within the house, based on outside sunlight and weather conditions.
After the initial bat box construction, you need to find or construct a sturdy pole to mount it. John Hatfield, of Wildlife Resolutions, an Ithaca, N.Y.-based pest control business that installs bat houses on all bat removal projects, likes pouring a simple concrete foundation, with c-channel anchors for support. Holes are then drilled through the c-channel and the pole is bolted in place. This way the pole base functions like a hinge, bat house can easily be erected or taken down as needed without the use of a 15- or 20-foot ladder. (See photos of pole mount.)
“When you consider building a bat box, prepping the site, then installing the pole and mounting everything, you’re looking at a weekend project, or a long weekend project,” Hatfield said, “but done right it will last 10 or 15 years with minimal maintenance.”
Bat Conservation International, a Texas-based non-profit that seeks to help bat populations in decline around the world, has collected, invented, and experimented with the very best of bat house designs. This two-chamber Rocket Box, so-called due to it’s rocket-like shape, is the largest of their designs recommended to small landowners and farmers looking for bat-based pest control. It’s also proved the most effective at recruiting and holding bat populations. This carpentry build is of moderate difficultly, requiring lots of predrilling and dozens of table or circular saw cuts. While not for the faint of heart, done correctly this build will last a decade or more, and provide sanctuary to hundreds of helpful pest eaters.
- 2-inch diameter steel pole, 20 feet long
- Two 1-inch by 4-inch by 8-foot boards
- Two 1-inch by 8-inch by 8-foot boards
- Two 1-inch by 10-inch by 6-foot boards
- 24-inch by 24-inch, 3/4-inch piece of AC exterior plywood
- Box of 100 exterior-grade screws, 1 5/8-inch
- Box of 100 exterior-grade screws, 1 1/4-inch
- 16 to 32 exterior-grade screws, 2-inch
- 20 to 30 roofing nails, 7/8-inch
- One-quart water-based primer, exterior grade
- Two quarts flat, water-based stain or paint, exterior grade
- Asphalt shingles or dark galvanized metal
- One tube paintable latex caulk
- Two 1/4-inch by 4 1/2-inch carriage bolts, washers and nuts
- Table saw or circular saw
- Caulk gun
- Tape measure
- Jigsaw, keyhole saw or router
- Sandpaper or sander
- Rasp or wood file
- Variable-speed reversing drill
- 1 1/2-inch hole saw or spade bit
- 1/8-inch and ¼-inch drill bits
- Screwdriver bit for drill
Bat Box Construction
- Measure, mark and cut out parts according to the template shown in Figure 1. Dimensions must be exact for correct. Cut out two vent slots and four passage holes as shown.
- Cut 1/16-inch deep horizontal grooves 1/4-inch to 1/2-inch apart on one side of all 36-inch and 45-inch boards and on both sides of all 42-inch boards. Sand to remove splinters. This creates the footholds that all bats require.
- Drill two 1/8-inch holes through each 3/4-inch by 1 1/2-inch by 4-inch block to prevent splitting.
- Assemble four pole sleeve boards into a hollow, square box as shown using 1 5/8-inch screws and caulk, as seen in Figure 2. Predrill holes to prevent splitting. Countersinking holes may also help.
- Attach spacer blocks to pole sleeve as shown in Figure 3 (four per side) using two 1 1/4-inch screws per block. Bottom spacer blocks are 9 inches up from bottom of pole sleeve. Top spacer blocks are 5 inches from top. Alternate spacer blocks on left and right sides, 5-inches apart.
- Assemble four inner shell boards into a hollow, square box as in step 4.
- Slide the pole sleeve into the inner shell until the top edges are flush with bat passage holes nearer the top. Mark the location of spacer blocks. Secure the inner shell to the pole sleeve with 2-inch screws through the spacer blocks to ensure that no screws protrude into the roosting chambers. Predrill holes to avoid splitting spacer blocks.
- Attach spacer blocks (4 per side) to inner shell as shown, using two 1 1/4-inch screws per block, as shown in Figure 3. Bottom spacer blocks are 10 inches up from the bottom edge of the inner shell. Top spacers are 4 inches from top. Alternate spacers left and right sides are 4 inches apart.
- Assemble four outer-shell boards into a hollow, square box as in step 4. Vent slots are on opposing sides and oriented towards the bottom.
- Slide the finished outer shell over the inner shell, so that 6 inches of inner shell protrudes below outer shell. Mark locations of spacer blocks. Secure outer shell to inner shell as in step 7.
- Caulking first, attach inner roof to box with 1 1/4-inch screws. Carefully drive screws into top edges of shells to prevent screws from entering roosting chambers.
- Center and attach outer roof to inner roof with 1 1/4-inch screws, caulking first.
- Paint or stain exterior at least three times using a good primer as the first coat. Cover roof with shingles or dark galvanized metal.
- Slide completed rocket box over pole. 1 inch up from the bottom edge of the pole sleeve, drill a 1/4-inch hole all the way through pole and sleeve. Rotate box and pole 90 degrees and drill another 1/4-inch hole, 2 inches from the bottom, through pole and sleeve. Secure box to pole with two 4 1/2-inch bolts, washers and nuts. Orient vent slots north and south during installation.
How To Keep Your Bat Box Full
According to the experts at Bat Conservation International, the most unused bat houses are mounted on trees, receive less than seven hours of daily sun, are not painted dark enough, or have roosting chambers wider than 3/4 of an inch.
If after at least one active season, your bat house remains unoccupied, try moving it to a new location where it receives more or less sun. Most successful bat houses are occupied within the first year, and most failure results from too little exposure to sun.
TO TREE, OR NOT TO TREE?:
With a canopy of branches and leaves, trees rarely provide enough sunlight to a bat house, or enough free drop space between ground and house for bats to fly in and out effectively. Move a tree-mounted bat house to the sunny sides of a two-story or taller building, or to the top of a 15- or 20-foot pole.
TURN UP THE HEAT:
This is one of the most important ingredients for a successful bat house, and probably the least understood. Unpainted bat houses and those mounted in the shade are seldom warm enough, and thus are rarely used. Unless you live in an exceptionally hot climate, you can help an under-heated bat house by moving it to a sunnier spot and painting it a darker color, after carefully caulking all exterior joints.
ROTATE WHEN NECESSARY:
If your house is mounted on a pole, try rotating it from a north/south exposure to east/west. Since unsuccessful houses tend to be too cool more often than too warm, this may help.
THE RIGHT PAINT JOB:
If your average high temperature in July is less than 85 degrees, paint the bat house black. If the average July high temperature is between 85 and 95 degrees, paint it a dark shade of gray or brown. Between 95 and 100 degrees use a medium shade. Over 100 degrees paint it a light shade of gray or brown.
Bats need open freshwater. Rivers, streams, irrigation ditches, lakes, ponds, and marshes are all good water sources. Saltwater and brackish water won’t help bats, nor will swimming pools or birdbaths. Bats drink in flight and require open space of at least 10 to 15 feet to fly through and drink.
This article is from the summer 2017 issue of The New Pioneer Magazine. Grab your copy at OutdoorGroupStore.com.
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