Something Runs in the Attic Right at Dusk

Timing settles it, and you can do this yourself tonight. Gray and red squirrels are daytime animals — noisy at dawn, active through the day, silent after dark. Flying squirrels are strictly nocturnal, so the noise starts within minutes of sunset, carries on through the night, and stops around dawn. That is the exact opposite pattern. The sound is different too: flying squirrels are small and light, so people describe fast scampering and soft thumps rather than the heavy rolling and loud gnawing of a gray squirrel.

Far more than you would guess from the noise. Flying squirrels den communally through the winter because huddling together conserves heat, and colonies of twenty to thirty in one attic are routine in this part of Wisconsin. This is the single most important thing to understand about the problem: it is not one animal that got in. It is also why people trap three or four, enjoy a quiet week, and then find the noise is back — because twenty-odd were left.

They glided. A flying squirrel has a membrane of skin between its wrists and ankles, and launching from a tall tree it can cover well over a hundred feet in a controlled glide, steering with a flattened tail. It never touches the ground and never climbs your wall. This is why the standard advice to trim branches back — genuinely useful against gray squirrels — helps far less here. You cannot stop a flying squirrel reaching your roof. You can only stop it getting through it.

About an inch and a half — roughly a golf ball — and they will enlarge something smaller by chewing. Being much smaller than gray squirrels, they exploit defects other squirrels simply cannot fit through: the corner where a soffit meets a fascia return, the gap behind a sagging gutter, a lifted shingle at a valley, damaged screening on a gable vent, the junction where a dormer meets the main roof. Plenty of houses that have never had a gray squirrel problem host a flying squirrel colony for years.

No. This gets confused with bats, which are seasonal. Flying squirrels are resident year-round. The winter group loosens as the weather warms and females separate to raise litters, but the site stays in use and they come back — and there are two breeding periods here, spring and late summer, so an occupied attic tends to become permanent rather than resolving on its own.

Trapping alone almost never resolves it, for two reasons. The numbers — removing five from a colony of twenty-five leaves twenty and the noise continues. And more importantly, trapping does nothing about the hole, so the site stays available and gets reoccupied, often the same season, because a warm dry insulated attic beside good habitat is prime real estate. Exclusion is what ends it: get every animal out, then seal the roofline properly.

Yes — when there are dependent young in the attic. Flying squirrels breed in spring and again in late summer, and sealing the adults out while non-mobile juveniles are still in the nest leaves them to die in your ceiling, which is inhumane and creates an odor and insect problem. Working out whether young are present is part of the inspection. Autumn is generally the best window: the late-summer young are mobile and the winter colony has not fully formed.

Mostly insulation, and it is worse than people expect because of the numbers. Colonies establish latrine areas rather than scattering waste, so you get heavily saturated patches of insulation with urine soaked through to the ceiling drywall below. Two winters of that ruins a substantial area. They are rodents with continuously growing incisors, so attic wiring is at risk too. And they carry the fleas and mites you would expect of any wild rodent, which disperse into living space when the colony is removed.

They are small, shy, strictly nocturnal animals with no interest in confrontation, and nobody is being attacked. The realistic concerns are the parasites they bring, which can disperse down into the house after the animals leave and cause unexplained biting, and the air-quality issue of accumulated droppings and urine-soaked insulation in an attic connected to your ventilation. Both are handled by cleaning up the site properly rather than stopping at animal removal.

We confirm the species by standing outside at dusk and watching the roofline — the emergence is so tightly synchronized that the animals show us the exit themselves within minutes of sunset. Then every other opening on the building is sealed with heavy-gauge hardware cloth, a one-way door goes over the remaining active entry, and the colony pushes out over several nights and cannot return. We monitor to confirm the attic is empty, seal the last opening permanently, and clean up the contaminated insulation and residual scent — which otherwise advertises the site to the next glider.