Bat Houses in Texas: Should You Put One Up When Bats Are Excluded?

When bats are sealed out of a Texas attic, many homeowners ask whether a bat house will give the colony somewhere to go. It can help, but only if it goes up early, is mounted in the right spot for Texas heat, and you are patient. Here is what TPWD, Texas A&M AgriLife and Bat Conservation International actually recommend.

The short version

A bat house does not remove bats. The colony still has to be let out of the building through one-way exits, and the gaps sealed. The bat house only gives the evicted bats a nearby option.
Put it up first. Bat Conservation International (BCI) says that when a bat house is paired with an exclusion, it should go up at least two to six weeks before the eviction if possible. TPWD and Texas A&M AgriLife both say to install alternative housing before the bats are excluded.
Exclusion timing still rules. TPWD discourages excluding bats from buildings from May 1 to August 15, when young can't fly and may be trapped inside.
Height, sun and clear space matter most. BCI recommends at least 12 feet of open space under the exits, morning sun, and keeping the house away from branches, wires and bright lights. In hot Texas summers, overheating is a real risk.
Expect to wait. BCI says some successful houses have taken as long as five years to be occupied, and some never are.

Why Texas biologists suggest a bat house before an exclusion

In a 2007 TPWD news release, TPWD bat biologist Meg Goodman put it simply: if you want to keep these insect eaters around, you can install a bat house near where they are living before evicting them, so that when they can't get back into the building they have an alternative roost. The same release describes the eviction itself as fitting the bats' exit holes with a smooth tube or netting they can leave through but not re-enter, leaving it about a week, and then sealing the openings permanently.

Texas A&M AgriLife's Bats in Schools program gives a Texas example of why this matters. It reports that after one Texas school district removed a bat colony without providing alternative housing, the bats moved into neighboring structures, causing problems for the neighbors. AgriLife says bat houses can make that less likely, but also that building alternative housing does not guarantee the bats will move in.

So a bat house is a reasonable add-on to an exclusion if you like having bats around your yard. It is not a lure that pulls a colony out of your attic, and it doesn't change how the building has to be sealed.

Timing a bat house around the Texas exclusion calendar

TPWD's Outdoor Annual says excluding bats from buildings is discouraged from May 1 through August 15, while young are unable to fly. That leaves two practical exclusion windows in most of Texas: late summer through fall, and late winter into spring before pups are born. AgriLife's Bats in Schools guidance puts the best eviction period at generally September through April, depending on where you are in the state, and notes that in cool weather (below 50°F) one-way devices should stay up at least 2 weeks instead of 1, because bats don't leave the roost on cold nights.

For the bat house, BCI's installation sheet says houses can go up at any time of year but are more likely to be used their first summer if they are installed before bats return in spring. A 2011 Texas Parks & Wildlife magazine how-to called early March the best time to install one. AgriLife notes that most Mexican free-tailed bats spend winter in Mexico and return to Texas in February or March, although Texas Tech's Mammals of Texas describes them as year-round residents in the eastern part of the state.

Putting that together: if your exclusion is planned for late summer or fall, the bat house should already be up by early summer at the latest. If you are sealing a house now, in late fall or winter, a bat house installed in the next few months will be in place for the spring return.

Which Texas bats use bat houses

The TPW magazine article reports that seven Texas species have been known to use bat houses, most commonly the Mexican free-tailed bat and the evening bat. Those are also two of the bats most often found in Texas buildings. Mammals of Texas says the evening bat roosts in hollow trees and attics, is common east of the 100th meridian, and has probably been served well by human development.

AgriLife adds that design has to fit the species: structures for Mexican free-tailed bats need an open-bottom design, and many commercially sold bat houses are unsuitable for North American species. For a colony being moved out of a building, AgriLife says alternative houses should be big enough for several hundred bats. A small single-chamber box on a fence post is not a replacement for an attic colony of that size.

Where to mount a bat house in Texas

BCI's current guidance, summarized:

On a building beats a pole, and a pole beats a tree. Wood, brick or stone walls hold daytime heat and release it at night. Bats rarely use houses on metal buildings or metal siding. Trees add clutter at the exits and give owls and raccoons easy access.
Height and open space. BCI's installation sheet says at least 10 feet above ground and 12 to 20 feet is better. Its guidelines call for at least 12 feet of open space under the exits so bats can drop into flight, and say higher is better, especially where outdoor cats are around.
Morning sun, afternoon relief. In warm southern climates, BCI says east-facing walls that get morning rather than afternoon sun are important, and that eaves, sunshades or awnings can shade a house. Its older installation sheet recommends 6 to 8 hours of direct sun on an east- or south-facing wall.
Away from perches and lights. Keep it 20 to 25 feet from tree branches and wires, and away from porch and security lights.
Not over doors, windows, patios or grills. Guano will drop below the house. BCI suggests placing it over a garden bed instead.
Near water helps. BCI notes most nursery colonies choose roosts within about a quarter mile of a stream, river or lake.

Texas heat: color, venting and chambers

Overheating is the main way a bat house fails or harms bats in Texas. The TPW magazine article reported that a bat house works best at an inside temperature of about 80 to 100 degrees, and that light colors should be used where July temperatures exceed 100 degrees, with dark colors only where July averages under 85. BCI's guidelines say a light shade is important in hot climates, and that vents in the lower third of the house help reduce overheating.

BCI now favors tall houses with four chambers over one- or two-chamber designs, because they offer a wider range of temperatures inside, and it suggests putting up at least two houses near each other, one warmer and one cooler, so bats can move between them. Roosting gaps should not exceed 1 inch. Use untreated, roughened wood and exterior water-based paint or stain on the outside only.

One design detail has changed over time. TPWD's small bat house plan for kids and older BCI designs line the back with plastic netting for footholds. BCI's current guidelines advise against installing screening or mesh on roosting surfaces because bats, especially young ones, can get trapped, and recommend roughening or grooving the wood instead.

What not to do

Don't catch bats and put them in the house. BCI says this does not convince them to stay and can injure them. Guano, scents and sound lures don't work either.
Don't use a flip-top box you can open, and never disturb an occupied house. Do maintenance, such as resealing seams or removing wasp nests, in winter after the bats have left.
Don't spray pesticides or herbicides in the yard around a bat house.
Don't handle bats. TPWD's Goodman noted that less than half of one percent of bats in natural populations get rabies, but Texas A&M AgriLife says bat bites should always be considered potential rabies exposures, and DSHS has guidance on when a bat should be captured for testing. Make sure pets are vaccinated.
Don't rely on a bat house instead of sealing. AgriLife's guidance is that the best way to keep bats out of buildings is to close every opening they use, down to about 3/8 inch.

Texas law in one paragraph

TPWD says bats may not be hunted, killed, possessed, purchased or sold, though they may be moved, trapped or killed if inside or on a building occupied by people, and exclusion is discouraged from May 1 to August 15. A bat house is the humane counterpart to that rule: you let the colony out at the right time of year, seal the building, and give the bats a place nearby if you want them to stay in the neighborhood.

Frequently asked questions

Will a bat house get bats out of my attic?

No. Bats have to be let out of the building with one-way exits and the openings sealed. A bat house only gives them a nearby alternative roost once they can't get back in, and there is no guarantee they will use it.

When should I put up a bat house in Texas?

Before the exclusion. Bat Conservation International recommends at least two to six weeks before the eviction if possible, and says houses are more likely to be used their first summer if installed before bats return in spring. A TPW magazine how-to named early March as the best time.

How high should a bat house be?

BCI says at least 10 feet above ground, with 12 to 20 feet better, and at least 12 feet of open space under the exits. Keep it 20 to 25 feet from branches and wires and away from bright lights.

What color should a bat house be in Texas?

Light to medium shades in most of Texas. A TPW magazine article said light colors should be used where July temperatures exceed 100 degrees, and BCI says light shades and lower vents help prevent overheating in hot climates.

Which Texas bats use bat houses?

TPW magazine reported seven Texas species have used bat houses, most commonly the Mexican free-tailed bat and the evening bat. Texas A&M AgriLife notes houses for Mexican free-tailed bats need an open-bottom design.

Sources

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