If you have bats in your Utah attic, there’s a good chance you have either a big brown bat colony, a little brown bat colony — or both. These two species account for the vast majority of bat infestations on the Wasatch Front and throughout Utah’s residential areas. Understanding which species you have affects the size of your problem, the urgency of action, and how your exclusion should be timed.
The Big Brown Bat (Eptesicus fuscus)
Identification
- Size: 4–5 inches body length, 12–16 inch wingspan — noticeably large for an attic bat
- Color: Glossy brown fur on back, paler underside, dark face and wings
- Flight: Slower, more deliberate flight pattern than little brown bats — often described as “fluttery”
- Droppings: Larger guano (½ inch), often found in scattered piles rather than dense accumulations
Behavior in Utah Homes
Big brown bats are year-round residents throughout Utah. Unlike some species, they don’t migrate — they may hibernate in your attic during winter, remaining in wall voids, insulation, and attic spaces through January and February. This means big brown bat infestations often go undetected through winter, only becoming apparent when the bats become active in spring.
Maternity colonies of big brown bats are typically smaller than little brown bat colonies — usually 20–300 females. However, they are one of the most common species to colonize structures, and their year-round presence means guano accumulates continuously.
The Little Brown Bat (Myotis lucifugus)
Identification
- Size: 3–3.5 inches body length, 8–11 inch wingspan — noticeably smaller
- Color: Glossy brown to bronze fur, lighter underside, distinctive shiny wing membranes
- Flight: Rapid, erratic, highly maneuverable — fast direction changes
- Droppings: Smaller guano (¼ inch), often found in very dense accumulations directly below large roost clusters
Behavior in Utah Homes
Little brown bats form Utah’s largest maternity colonies — sometimes hundreds to over a thousand females in a single structure. They prefer warm attics with consistent temperatures and can raise attic temperatures significantly in large colonies. Little brown bats typically migrate or hibernate in caves and mines during winter, returning to the same attic roost every spring.
Because little brown bat colonies are larger, guano accumulation is faster and more concentrated. A 500-bat little brown bat colony can contaminate an entire attic’s insulation within 2–3 seasons.
Does the Species Matter for Removal?
For the exclusion process itself, not dramatically — one-way exclusion works on both species. However, species identification matters for:
- Colony size estimation: If you have little brown bats, expect a larger colony (and potentially larger guano cleanup) than with big brown bats
- Winter activity: Big brown bats may be present and active in your attic during winter — little brown bats typically aren’t. This affects winter inspection and exclusion timing
- Endangered species compliance: Some Myotis species (closely related to the little brown bat) are listed or candidate species. Species identification ensures our work is fully compliant
- Maternity season timing: Both species are subject to Utah’s May 1–August 15 exclusion restriction, but pup development timelines vary slightly between species
How We Identify Your Bat Species
During our free inspection, our licensed technicians identify your bat species through direct observation at entry points at dusk, examination of guano characteristics, and assessment of colony activity patterns. This identification is included in our written inspection report and informs our exclusion plan.
Call for a free inspection: (801) 675-8829
Utah Wildlife Specialists — Licensed by UDWR | 15+ years | Serving all of Utah
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