Jodi Doxrude lives near a river and a nature preserve, so she wasn't surprised to see occasional bats near her house. But when they started flapping around guests at an outdoor birthday party for her husband in May, she got suspicious.
Noticing odd bulges in their house's cedar siding, the Doxrudes removed a plank to check it out.
"That's when all the bats flew out. It was like Scooby Doo," Doxrude said. "There were about 60 bats that flew out of there. … My husband and brother-in-law almost hit the roof."
In all, the Doxrudes found between 300 and 500 little and big brown bats living in the space between the siding and the exterior wall of their Stevens Point, Wis., house. The bulges were caused by deposits of bat guano that had built up over the years as the bat colony grew, pushing parts of the siding outward.
The first of the bats likely moved in some previous fall — when bats, birds, spiders, scorpions, mice, rats, raccoons, snakes and squirrels tend to fly, gnaw or creep into suburban attics and basements.
You might call this time of year the critter season — when humans and certain animals collide. Even large animals, such as mountain lions and bears, have been known in rare cases to seek shelter for short stretches under more secluded homes.
"When the temperatures change, this is when animals generally seek refuge wherever, and houses often provide those refuges," said Peter Weigl, a professor of biology at Wake Forest University in North Carolina who studies animals, especially flying squirrels, taken from people's homes.
Nocturnal flying squirrels are hard to spot in the wild, but often not hard to hear in a house, scraping or rolling acorns overhead.
"This is the time of year that I frequently get calls from people about flying squirrels that apparently have set up a bowling league in the attic," Weigl joked.
Ants, cockroaches and termites remain the most common household pests, but some observers believe greater numbers of medium-sized animals may want into private homes these days. With suburbs encroaching on the wild and thinning the ranks of large predators, they theorize, animals like raccoons, opossums and skunks may reproduce more quickly.
"Their numbers are exploding, so they're coming into our habitats," said Terry Root, a senior fellow at the Center for Environmental Science and Policy at Stanford University.
Weigl has heard of people keeping flying squirrels as pocket pets. But cute or not, when things go bump in the night, even mild-mannered nature lovers and pacifists can turn bloodthirsty.
"If you're upstairs in your bedroom and you hear scraping, you don't know whether you've got mice, squirrels, a burglar, bats … you want it out of there," said Cindy Mannes, director of public affairs for the National Pest Management Association. "It really does change human behavior, and any pest control company will tell you this."
Mike Rottler, president of Rottler Pest Control in St. Louis, said his brother, who handles wildlife cases, once visited a Missouri convent where nuns heard animals in the attic. He set traps for garden-variety squirrels, which can gnaw their way into homes. But after another night of noises, the head of the convent wanted blood.