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FIELD GUIDE

The mouse in the muffins

The white-footed mouse is a forest mouse.Marion Larson/Mass Wildlife

One night in the spring of 2020 I stopped by my parents’ house for a visit. I was standing in the kitchen when I heard a scratching noise on the counter behind me. I turned around and was surprised to see a mouse trapped in a plastic container of corn muffins.

The little rodent must have squeezed under the lid and then became stuck inside. Mice are notorious for being able to squeeze through tight spaces. I picked up the container to take a closer look, and the mouse began to panic, scrambling to find a way out. But, after a minute or so, it ignored me and began nibbling on a corn muffin.

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I took a short video and a few photographs of the mouse, showed it to my parents, then turned it loose in their yard. When I shared the video, I misidentified the mouse as a house mouse. But my friend and colleague, Larry Kelts, professor emeritus in the biology department at Merrimack College, correctly identified the species as a white-footed mouse, Peromyscus leucopus.

The house mouse, Mus musculus, introduced from Europe and central Asia, is smaller and uniformly grayish-brown in color, he explained, while the white-footed mouse, which is about 3 to 4 inches long with a tail almost as long as its body, has large, round ears, big, dark eyes, and brownish fur, with a white belly and white feet.

Tom French, retired assistant director of MassWildlife’s Natural Heritage & Endangered Species Program, said that in addition to the white-footed mouse, Massachusetts has a few other native species, including the deer mouse — which tends to be found more in the western part of the state — and two species of jumping mice: the meadow jumping mouse and the woodland jumping mouse, both of which have big hind feet, long tails, and true to their name, jump around like kangaroo rats.

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The house mouse is Massachusetts’ only introduced mouse species, French explained.

“In the north, they’re confined to urban settings,” said French. “They’re the subway mouse in Boston. If you’re sitting and waiting for the subway, and you see a mouse, it’s a house mouse.”

In Boston, Cambridge, and Somerville, you’re going to get the house mouse, said French. But anywhere away from the city, the white-footed mouse takes over.

“The white-footed mouse is ‘the mouse,’” said French. “The standard Massachusetts mouse, the mouse that comes into people’s houses in winter.”

A white-footed mouse crawled into a container of corn muffins at Don Lyman's parents' house in May of 2020.Don Lyman

The white-footed mouse is a forest mouse, French explained, so if you have trees around your house, especially oak trees, which produce acorns — one of the white-footed mouse’s favorite foods — you’re likely to have white-footed mice in your yard and house.

In the fall and winter, white-footed mice and flying squirrels tend to come into people’s houses to get warmth and shelter from the weather, said French. Flying squirrels usually will hang out in the attic, but white-footed mice tend to live in the walls, and they’re good climbers, so they can go up and down to all floors, from the basement to the attic. French said he trapped a dozen house mice on the 19th floor of his former office building in downtown Boston.

Four young white-footed mice were found nesting in a plant pot.Marion Larson/Mass Wildlife

White-footed mice even come into your car, said French. He said his son, who is a mechanic, sometimes finds piles of acorns in car air filters and heating ducts. Mice will also chew wires, and sometimes make nests in car engines.

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“Twice I had a mouse come out onto my windshield where the windshield wipers are,” said French. “And I had mice pooping all over my car. I even thought of setting mouse traps inside the car.”

French said white-footed mice are cute, so he’ll generally tolerate them, even in his house. But if they start chewing on upholstery, bringing acorns inside, and pooping and peeing all over, that’s a problem.

In this part of the country mice don’t pose much of a risk of transmitting diseases to humans, French said. They can carry hantavirus, which can cause respiratory illness, but it’s very rare. According to the Centers for Disease Control and Prevention, from 1993 to 2019, 816 cases of hantavirus were reported in the United States. Only six of those cases occurred in New England, and there were no reported cases in Massachusetts.

French said in general it’s a good idea to avoid contact with mouse droppings, or any animal droppings, because that’s where parasites and their eggs are found.

White-footed mice can be vectors for Lyme disease, French explained. They don’t transmit the disease directly to humans, but many white-footed mice have the Lyme bacterium, Borrelia burgdorferi, in their blood. If larval deer ticks feed on the blood of infected white-footed mice, the ticks can then spread Lyme disease to humans if the ticks later bite people. You can’t control the mice enough to control ticks with Lyme disease, said French, but you can use tick repellants and check yourself for ticks when you’ve been working in your yard or have been engaged in other outdoor activities.

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French advises people not to use rat and mouse poisons, because they travel through the food chain, and can affect animals that feed on the poisoned rodents. Rodent poisons are usually anticoagulants, which cause rats and mice to bleed to death, and they can have the same effect on animals that eat poisoned rodents.

“The poison makes the mouse wobbly while it’s dying,” said French, “and if a rat or mouse is wobbling down the street, no hawk or owl in its right mind will pass that up.”

Eating poisoned rodents is one of the leading causes of death for hawks and owls, French said.

Two bald eagles died after ingesting rat poison in Middlesex County in 2021, one in March and another in July.

Old-fashioned mouse traps are as good as rat poison, French said, and a lot safer for wildlife.

Some people use live traps, then release the mice into the wild. Dave Taylor, a retired high school science teacher and licensed wildlife rehabilitator, said he has been live-trapping mice in his house during the winter for many years.

“I use a mouse-size Havahart trap baited with peanut butter,” said Taylor.

Taylor said he keeps the mice in a 10-gallon aquarium until spring, when he releases them outdoors. But you shouldn’t release them close to your house, he advised.

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“I read that they have to be released at least 2 miles away as they can readily find their way home if released any closer,” said Taylor.

Mice are on the menu for all sorts of wildlife, including weasels, foxes, and coyotes, said French.

“Coyotes can take down a deer,” said French. “But coyotes eat a lot of mice and chipmunks. Mice are the support base for a lot of predators. Barred owls live off of white-footed mice.”

And there are plenty of mice to eat, said French. White-footed mice tend to breed in spring, summer, and fall. Females have two to five litters a year, with a typical range of two to six offspring per litter.

White-footed mice nest underground in other animals’ burrows, said French, or in cavities in logs or trees. Mice are good climbers and will sometimes nest in birdhouses, or high up in trees in woodpecker holes.

According to “Peterson’s Field Guide To The Mammals Of America,” white-footed mice are found from southern Canada, throughout most of the eastern and central U.S., and south into eastern Mexico. They can live two to three years in the wild.

Like all rodents, mice have two prominent incisor teeth in their upper and lower jaws that they use for gnawing. And they use them to good effect. Indoors, I’ve had mice chew their way into bags of walnuts, Doritos, and doughnuts, as well as chocolate candy — Hershey’s dark chocolate with almonds and Reese’s Peanut Butter Cups seem to be favorites.

In the wild, white-footed mice feed on acorns, fungi, berries, and new plant growth, as well as insects, said French. They also gnaw on the bones of dead animals, as well as on shed deer antlers.

“They’ll even eat little newly hatched warbler chicks,” said French. “That’s one of the reasons they’re so successful. They’ll eat anything. White-footed mice never run out of food.”

Don Lyman is a biologist, freelance science journalist, and hospital pharmacist who lives north of Boston. Send your questions about nature and wildlife in the suburbs to donlymannature@gmail.com.