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.
"She said, 'I want you to get rid of whatever's in this attic. I want you to get a gun and shoot it. And when you shoot it. I want to see it to make sure it's dead,'" Rottler said. "We typically tried to trap, but in this situation, that wasn't going to be good enough for her."
Rottler recalled his brother reluctantly went upstairs with a .22-caliber gun and shot dead the culprit — a raccoon.
Such drastic measures may not be legal everywhere, or may require special permits.
Greg Baumann, the NPMA's technical director, recalls a Maryland house whose owners heard scratching in the walls. The mystery ended during a noisy New Year's Eve party, when panicked flying squirrels popped out and started ricocheting around the house, as the host and guests chased them with fireplace tongs.
Baumann, who got the call the next day, said driving out the flying squirrels was tricky. They were locally protected, making it illegal to trap or kill them.
Some people have more tolerance for creatures in their midst than the angry nun or the tong-waving partygoers.
A man in a wooded area of Missouri didn't seek help despite regularly seeing venomous copperhead snakes in his yard — until one day a baby copperhead started doing laps with the man's wife in an indoor swimming pool. Rottler found snakes nesting nearby under the house's patio.
A woman in a swampy part of southern New Jersey knew she had a black rat snake or two living in her basement for seven or eight years, but figured they were not dangerous to people and killed other pests. It was only when one slithered from under a living-room hutch during a cocktail party that she grew embarrassed and decided to act.
"We ended up removing 33 snakes," said David Fisher of the company J.C. Ehrlich. "I've been in the business for 20 years and the most I've run into in a house was six or eight."
"Everybody's tolerance level for any pest is different," Fisher added. "I would have called when I saw the first snake in the basement. I would not have waited until my guests saw it."
Few people would. Panicked homeowners typically confuse harmless snakes with rarer venomous ones, and carry out bloody executions before exterminators even arrive, professionals say.
"The thing I would probably fear in my house more than anything else would probably be a wasp," said Craig Tufts, chief naturalist at the National Wildlife Federation in Reston, Va., adding it is rare for most larger animals in homes to attack unprovoked.
Still, there can be dangers besides stingers or venom to having outdoor animals in homes. Some can bring disease, noise, odor, parasites, or harm to infrastructure, property or pets.
Experts say homeowners can take measures to critter-proof their house by plugging even small holes in attics and foundations, screening over exhaust vents and chimneys, and obstructing areas that could shelter birds or bats. Some suggest dehumidifying basements to keep snakes and insects out, or putting mothballs in attics to repel flying squirrels and other unwanted guests.
"If your house is providing those really good habitats for those critters, they're going to take advantage of it because they're opportunists," Tufts said.
Tufts, an adviser for the NWF's Backyard Wildlife Habitat Program, suggests creating or restoring outdoor animal habitats in residential neighborhoods so pests are less tempted to break into our warm, cozy homes.
That's the approach Doxrude is taking with her bats.
"It was to the point where we couldn't even go outside," said Doxrude, 32, who has two young children. "[The bats were] screaming at you. They would swoop down at you."
To get rid of the bats, the Doxrudes replaced their siding and removed the asbestos beneath it. Then, at the urging of a local naturalist, Dino Tlachac, they donated the old cedar siding and bat guano to build bat houses in a nature preserve on their street.
"They already have the scent of the bats," Tlachac said. "They think they're at the same house, because we use the same wood."
Amid West Nile virus, Doxrude and some of her neighbors don't mind sharing the area with the mosquito-killing bats.
"They'd rather have them living in the bat houses than in our house or their house," Doxrude said. "They [the bats] are very beneficial. We like them around."