Fall Bat Swarming in Utah
DWR says bat encounters often spike in September as migratory species—especially Mexican free-tailed bats—move through Utah. Here is what that means for homes, pets, and exclusion timing.
Why September feels like bat season in Utah
Most people connect bats with Halloween, but Utah Division of Wildlife Resources (DWR) staff say you should expect activity through summer and a second wave in early fall. In a July 14, 2026 DWR news release, Mammal Conservation Coordinator Kimberly Hersey explained that encounters with bats seem to spike in September as migratory species—especially the Mexican free-tailed bat—move around Utah.
Utah is home to 18 confirmed bat species. Five of them migrate each year: they fly south from late August through October and return in April and May. Other species hibernate in caves, mines, or cliff crevices, often alone or in small groups rather than the huge eastern hibernacula people picture.
Mexican free-tailed bats also mattered in Utah’s 2024 rabies numbers. The Utah Department of Health and Human Services (DHHS) recorded 31 rabid animals statewide—all bats—and Mexican free-tailed bats accounted for 10 of those positives, the largest single-species share.
Migration is not the same as a maternity colony
Summer attic problems are usually maternity colonies: females move into buildings in May or June to give birth, and June through August is the hardest window because flightless pups depend on returning mothers. DWR does not permit colony removal then unless there is a human health and safety issue, and it advises against sealing openings from May through August.
Fall swarming and migration are different. Migratory bats are moving through the landscape, resting in night roosts, and sometimes briefly using buildings as they travel. That is why homeowners report more one-off indoor bats in September even when they never had a summer colony. It is also why fall—after pups can fly—is the season DWR names for permanent sealing and one-way exclusion netting.
Salt Lake County Health Department’s bat brochure is stricter on the calendar: do not use exclusion methods from May 1 to September 1. Once that county window ends, and after August under DWR’s statewide guidance, a permitted wildlife nuisance control company can coordinate humane exclusion and seal the gaps bats use at ridge vents, chimneys, and rooflines.
What to do if a bat shows up indoors this fall
- No contact suspected: Open a door or window, turn lights off inside, turn a porch light on, leave the room, and let the bat leave on its own.
- Contact possible (bite, scratch, or bat in a room where someone slept): Do not release or dispose of the bat. Contain it under a box without touching it and call animal control and your local health department so testing can be considered.
- Pets: Separate the pet from the bat, call animal control, and talk with your veterinarian about the pet’s rabies vaccination status. Utah’s rabies rule (Utah Admin. Code R386-702-12) says dogs, cats, and ferrets should be vaccinated, and cities and counties that license pets must require it.
Never handle a bat with bare hands. DWR’s gloved container-and-cardboard method is for situations where the bat will not leave on its own and contact has already been ruled out with health officials when needed.
Prevention while migrants are moving
DWR’s prevention list still applies in fall: cool the attic with fans, inspect siding, chimneys, and rooflines, and seal cracks with caulk, hardware cloth, foam, tar paper, or chimney caps—after the maternity window. After August, DWR describes hanging bird netting over an exterior opening (stapled at the top and sides, open at the bottom) for four to five days so bats can leave but not return, then sealing the holes.
Wasatch Front cities from Salt Lake County south into Utah County see both summer maternity roosts and September migrant traffic. If you already know bats used your attic last summer, schedule a fall inspection once the local no-exclusion window has closed rather than waiting for next May.
Common questions
Why do Utah bat sightings spike in September?
Utah DWR mammal coordinator Kimberly Hersey says encounters seem to spike in September as migratory species—especially the Mexican free-tailed bat—move around Utah. Five Utah bat species migrate south from late August through October and return in April and May.
Are Mexican free-tailed bats common in Utah rabies cases?
Yes. Utah DHHS’s 2024 rabies annual report recorded 31 rabid animals statewide, all bats. Mexican free-tailed bats were the largest share of those positives (10), followed by big brown bats (7) and western pipistrelles (6).
Does fall swarming mean I should seal my attic in September?
Fall is the best season for exclusion after pups can fly. Salt Lake County’s bat brochure still says not to use exclusion methods from May 1 to September 1. After September 1 (and after August under DWR’s statewide guidance), permitted exclusion and sealing can proceed when no human health emergency exists.
What should I do if a bat is inside during fall migration?
Never handle a bat with bare hands. If no contact is possible, open a door or window, lights off inside, porch light on, leave the room. If anyone may have had contact or slept in the room, contain the bat without touching it and call local animal control and your health department.
Is killing bats legal during fall migration in Utah?
No. DWR says bats are protected wildlife and it is illegal to kill them. Use a permitted wildlife nuisance control company that coordinates timing with DWR.
Related city guides
- Salt Lake City bat removal
- Murray bat removal
- Saratoga Springs bat removal
- Lehi bat removal
- Herriman bat removal
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