Ah, fall! Colorful leaves, pumpkin spice lattes, football — and mice infestations.

Those curious little rodents that spent the summer foraging outdoors are now looking for a warm place to cuddle up and nest before chilly weather takes hold.

"We call it the fall invasion," said Dion Lerman, an environmental health program specialist for the Pennsylvania Integrated Pest Management Program. "They follow plumes of warm air coming out of our homes that also carry food scents on them."

About 85 percent of homes in the country, regardless of how modest or elegant, how clean or dirty, have had a mouse run through in the last six months.

Mice can get though a gap the size of a dime; rats need a quarter's worth of space. They favor out-of-the-way spots such as the inside of walls or underneath floors. They also like corrugated cardboard boxes that aren't moved much, such as the ones filled with family mementos and stored in the attic or basement, Lerman said.

"They wait until there is no more sound from the plumbing system and then they come out and do their mousy thing," said Lerman. They tend to nibble on 30 different food items a night. Grease on a stove is a favorite for mice, ditto for cockroaches, he said. Those Doritos crumbs you no longer notice beneath the sofa cushions? Mice see them just fine.

Right now, business is good, said Charles Evans, owner of Evans Pest Control, which services residential and commercial locations in Philadelphia. They are seeing about 40 to 50 first-time clients a week, he added.

Because most rodents tend to hide when people are about, the first indicators are the telltale droppings they leave behind. Mice droppings are about the size of a grain of rice. Rat feces look like raisins with blunt edges, Evans said.

Mice mature in 30 days and can have four to six pups at a time. With a gestational period of 28 to 30 days, they can multiply quickly, which is why it is best to contact a professional for a rodent infestation. The rodents' rapid reproductive rate — and wily behavior — will often outpace any homeowner's attempt to control them, Evans said.

Jim Fredericks, chief entomologist with the National Pest Management Association, and a Philadelphia native, said that older, East Coast cities are likely the most rodent-infested locations in the country, because older buildings and underground infrastructure can be easier to get into. Higher housing density means more people — and more sanitation challenges — that set the stage for rodents, Fredericks said.

The health implications can be serious, he said.

"When a rat climbs out of a toilet and runs into the kitchen, you can only imagine what it is carrying on its feet and fur," said Fredericks. There are food-borne illnesses as well as higher asthma and allergy rates – especially in children – that correlate with rodent and roach infestations, he said.

The urine, which tends to dribble out as the rodents scamper along room edges, is also a source of disease and must be cleaned up, he said.

The Norway rat or common brown sewer rat is well-adapted for any climate. House mice tend to be the kind found in the city while it is deer mice or white-footed mice that get into suburban homes, he said.

If you think having a cat or dog will discourage rodents, think again.

"Modern pets are too well-fed and aren't really highly motivated," said Lerman. "They might think the mice are fun, but the [the rodents] are not perceived as something to eliminate."

Pet food, however, will attract rodents. If you are leaving food out at night for the dog or cat, you are also leaving food for mice, said Lerman.  Mice may also steal kibble and move it someplace safe, such as your winter boots, so they can eat it later, he said.

If you are taking the do-it-yourself route for catching the critters, what kind of trap you use will matter. Cotton balls soaked in peppermint oils may seem an environmentally friendly solution, but the experts say mice will just walk around them.

Evans prefers the old-school wooden Victor snap traps. And while the squeamish among us might dispose of the trap and its occupant together, he suggests reusing the traps because the pheromones that were emitted by the previous mouse will attract others.

"You will have better success trapping them on an old trap than a new trap," he said.

Lerman is partial to Trapper's Mini-rex or T-rex traps, which can also be reused.

Those glue traps that are a favorite in some day-care centers can be problematic. The sticky adhesive usually catches but doesn't kill younger mice. They are discovered just about the time the facility opens for the day, he said.

"The little mice are screaming, the kids start crying, the parents freak out, and the staff freaks out," Lerman said. "And, it is all at 6 a.m."

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