Bat maternity season is the one time of year when you legally cannot seal bats out of your home , and for good reason. From late spring through summer, mother bats care for flightless pups in attic colonies.
Sealing the entry points during this window traps the babies inside , installing a bat house nearby provides an alternative roost, where they starve, die, and create a secondary infestation of flies, odors, and health hazards.
This guide explains when maternity season runs, why exclusion is off-limits, and how proper attic exclusion works during the legal window.
Disclaimer: Bats are protected under federal and state wildlife laws in most jurisdictions. The Endangered Species Act (ESA) and state fish and wildlife regulations prohibit the killing, harassment, or disturbance of bats during maternity and hibernation seasons.
Always consult a licensed wildlife professional before performing any bat exclusion work.
Key Takeaways
- Maternity season runs May through August: Exact dates vary by species and region, but most bat pups are born and raised during the warm months. Sealing your home during this period is illegal in nearly every state.
- Exclusion traps flightless babies: Newborn bats cannot fly for 3 to 6 weeks. Blocking their exit seals them inside, where they die. The carcasses attract flies, beetles, and create health risks.
- You can still inspect, monitor, and prepare: Maternity season is the ideal time to identify entry points, observe bat behavior, and ready exclusion materials so you act the day it becomes legal.
- Exclusion resumes in late summer to early fall: Once pups are flying (typically mid-August through September), one-way doors and sealing work can begin. This window closes again before hibernation.
When Is Bat Maternity Season?
Bat maternity season generally spans May through August in most of the United States, but the exact timing depends on your region and the bat species roosting in your attic.
Little brown bats (Myotis lucifugus) and big brown bats (Eptesicus fuscus) , the two species most commonly found in residential attics , typically form maternity colonies from June 1 through mid-August.
Mexican free-tailed bats (Tadarida brasiliensis) begin earlier, from mid-May through early August. Evening bats (Nycticeius humeralis) can start as early as late April, with pups fledging by mid-July.
Regional variation is significant. Florida’s maternity season runs April 15 to August 15. Connecticut and other northeastern states observe early May through mid-August.
Some states like New Hampshire restrict exclusion work from mid-May through mid-August. Always check your state fish and wildlife agency’s specific dates before scheduling any work.
Female bats typically give birth to one or two pups in late spring. The pups nurse for 3 to 4 weeks and begin taking short practice flights around 4 to 6 weeks of age. They are not fully independent until they can forage on their own, which takes another week or two after their first flights.
Why You Cannot Exclude Bats During Maternity Season
Babies Cannot Fly
Newborn bat pups are entirely dependent on their mothers. They are born hairless, blind, and incapable of flight for the first 3 to 6 weeks of life. If you seal the entry points while the mother is out foraging at night, you trap the pups inside the attic.
The mother may try frantically to re-enter , circling at dusk, crawling along rooflines, and calling for her young , but she cannot get back in. The pups die of dehydration and starvation within days.
Trapped Pups Create Sanitation Hazards
Dead bat pups in an enclosed attic space decompose rapidly. The carcasses attract carpet beetles, dermestid beetles, phorid flies, and other scavengers that can then infest the rest of your home. The smell of decomposition can linger for weeks and often requires professional odor remediation even after the carcasses are removed.
Legal Penalties Are Severe
Bats are protected under multiple layers of law. The federal Endangered Species Act (ESA) prohibits the taking, harassment, or harm of any listed bat species , including the Indiana bat (Myotis sodalis) and the northern long-eared bat (Myotis septentrionalis).
Penalties under the ESA can reach $50,000 or more per violation, and repeat offenses can carry criminal charges including imprisonment.
Even for non-listed species, most state wildlife agencies prohibit bat exclusion during maternity season. Homeowners who seal entry points during this window can face civil fines, mandatory remediation orders, and in some states, forfeiture of the property structure as evidence in wildlife violation cases.
What You Can Do During Maternity Season
While you cannot exclude bats during maternity season, you can take several steps that do not disturb the colony and set you up for a fast, effective exclusion the day it becomes legal.
Conduct an Exterior Inspection
Walk the perimeter of your home at dusk and watch where the bats exit. Common entry points include loose soffit vents, ridge cap gaps, gable end vents, chimney crowns, gaps where siding meets the roofline, and uncapped plumbing vents.
Make a list of every gap, crack, or opening larger than 3/8 inch (about the width of a pencil eraser). Bats can squeeze through surprisingly small gaps.
Monitor Bat Activity
Count how many bats emerge each evening and how long the exodus takes. A small colony (10 to 30 bats) can often be excluded with DIY methods once the season ends. Larger colonies (100+ bats) typically require professional intervention. Note the entry points on a diagram of your roofline so you remember exactly where to work.
Install a Bat House
Installing a bat house on your property before exclusion gives the colony a safe alternative roost. Place the bat house on a pole or the side of a building, 12 to 20 feet off the ground, facing south or southeast for maximum sun exposure.
Position it at least 25 feet from the main entry point your bats are using. Bat houses are inexpensive, widely available, and can increase the odds that the colony relocates successfully rather than trying to force its way back into your attic.
Gather Exclusion Materials
Stock up on the materials you will need: 1/4 inch hardware cloth (the standard for bat exclusion), galvanized steel mesh, high-expansion foam designed for pest blocking, caulk, and a bat valve or one-way exclusion door.
Having everything on hand means you can seal the home the same day exclusion becomes legal in your state, before the window closes for hibernation season.
When Exclusion Can Resume
Bat exclusion can typically resume once the pups are flying and the maternity colony begins to break apart , usually mid-August through late September, depending on your region and the bat species.
For little brown and big brown bats (the most common attic dwellers), the exclusion window opens around August 15 and runs through late September or early October.
Mexican free-tailed bats and evening bats may fledge earlier , as early as late July in warmer climates. Before the maternity season ends, confirm with a wildlife professional that no pups remain inside. If you see bats still entering and exiting at dusk in early August, wait another week or two.
The preferred method is a one-way exclusion valve: a device fitted over the entry point that allows bats to leave but prevents them from re-entering.
After 3 to 5 days of no activity, the valve is removed and the gap is permanently sealed with hardware cloth and caulk. After exclusion, be thorough about cleaning the guano accumulation and sanitizing the attic space.
After mid-October, bats in most of the United States begin entering hibernation (torpor) in caves, mines, and other protected sites.
Attempting exclusion during hibernation is also illegal in many states because disturbing torpid bats can kill them. If you miss the late-summer window, wait until the following spring after the colony leaves the maternity roost.
Frequently Asked Questions
Can I remove a single bat I find in my living room during maternity season?
Yes. A single bat that has entered your living space can be safely removed (wear thick leather gloves, contain it in a box, and release it outside at dusk).
This is not considered exclusion or colony disturbance. If you find multiple bats inside the living area, it may indicate a larger roost issue that requires professional assessment.
How do I know if bats are roosting in my attic?
Common signs include squeaking or scratching sounds from the attic at dusk and dawn, small dark droppings (guano) accumulating on exterior walls or window sills, a strong ammonia smell near entry points, and dark staining around soffit vents or roof edges where bats enter.
You may also see bats emerging at sunset if you watch the roofline from outside.
What happens if I accidentally seal a bat inside during maternity season?
Contact a licensed wildlife professional immediately. Do not unseal the area yourself , you may allow more bats in.
A professional can install a one-way exit device that lets the trapped bat escape while preventing re-entry. The cost of emergency remediation is significantly higher than planned exclusion, which is why preparation during the waiting period is so important.
Do bat houses really work as an alternative roost?
Yes, when properly installed. Bat houses positioned 12 to 20 feet high on a south or southeast-facing structure, receiving at least 6 to 8 hours of direct sun, have occupancy rates above 80 percent in well-chosen locations.
Adding a bat house before exclusion gives the displaced colony a ready alternative and reduces the chance that they attempt to re-enter your attic or find their way into a neighbor’s home.
Is DIY bat exclusion ever safe?
For small colonies (under 30 bats) with a single, accessible entry point, DIY exclusion after maternity season is possible if done correctly with one-way valves and proper sealing materials.
For larger colonies, high roosts, or bats in wall voids or chimney spaces, professional exclusion is strongly recommended. Errors in DIY exclusion , sealing bats inside, missing secondary entry points, or working during the protected season , can lead to dead animals, legal trouble, and costly repairs.
Related Resources
Plan your exclusion with bat exclusion products and see bat removal costs.
When it is safe to exclude, our bat in the attic guide walks you through the process. For pro guidance, read DIY vs Professional Wildlife Removal.
Why Trust Us
WildAnimalsCentral.com is an independent wildlife education and pest control resource. Our content is researched from state fish and wildlife agency publications, federal guidelines under the Fish and Wildlife Service, and interviews with licensed wildlife control operators.
We do not provide legal advice; bat protection laws vary by state and municipality, and they change as new species are listed under the Endangered Species Act. Always verify your local regulations with your state wildlife agency or a licensed professional before taking action.
Disclaimer: The information on this page is for educational purposes only and does not constitute professional wildlife control or legal advice. Laws regarding bat exclusion vary by state and species. Consult a licensed wildlife control operator and your state’s fish and wildlife agency before performing any exclusion work.
