Deer mice: Home invasions have begun

Every fall, shortly after nighttime, temperatures turn chilly and deer mice seek refuge from the coming cold weather by moving into our homes. They are usually a bigger problem in older rural houses, but deer mice live everywhere and can even infest suburban homes.

Mice invasion

I knew the season had arrived just a few nights ago while listening to a Pirates game. A deer mouse scampered boldly across the living room floor.

Deer mice are endearing little creatures with rich brown fur, big ears, big dark eyes, and a long tail. But nobody wants to live with mice all winter long. They move into houses because it’s warm and dry, and there’s usually food available. Pretzel crumbs and pizza crusts can send a deer mouse into a feeding frenzy.

Breeding

And well fed mice can breed all winter long. A single pair of deer mice can produce more than 20 babies during the winter, and each of those offspring is reproductively mature at eight weeks of age. Furthermore, females ovulate immediately after giving birth, and usually become pregnant while nursing the previous litter. Do the math, and you’ll discover that mice can reproduce exponentially.

After a gestation period of 23 days, three to seven young are born. They are pink, naked, blind, and helpless. The pups grow rapidly and wean at three-and-a-half weeks. At eight weeks of age, they are sexually mature. Adults can produce up to four litters per year.

The high reproductive rate is offset by an average life span of less than a year.

Wild mice

In the wild, deer mice spend much of their time on or below the surface of the ground, but they climb trees easily. They build nests in subterranean dens, under logs and rocks, as well as in tree cavities as high as 50 feet above ground.

One reason deer mice are so ubiquitous is that food is usually abundant. They eat seeds of many common grasses and weeds and a wide variety of berries, nuts, buds, and fungi. During the summer they eat everything from gypsy moth caterpillars, grasshoppers, and crickets to an occasional egg or baby bird.

In the fall deer mice store vast quantities of seeds and nuts in cache sites as varied as hollow logs, tree cavities, nest boxes, and even old bird nests. I’ve often found an old robin nest filled with a mound of dried leaves. Inside, I usually found a generous supply of small seeds.

Because deer mice do not hibernate, these food caches come in handy during the winter.

Bottom of food chain

Fortunately, deer mice have one important redeeming quality. Almost every predator eats them. They form an essential link in the complex, interconnected food chains that make up virtually every terrestrial ecosystem. Though deer mice eat primarily plant material, they are prey to a tremendous variety of predators — snakes, hawks, owls, weasels, raccoons, skunks, bobcats, coyotes, and foxes.

Deer mice are thus the ecological link in the food chains that connect plants to carnivores. But they can only do that when they live outdoors.

Mice control

Indoors, mice wreak havoc. Over the years I’ve tried many methods to control mice.

Poisons can harm anything that gets into them, including children and pets. Glue traps are cruel. Sonic repellents do not work. That leaves the old fashioned snap trap. Though the U.S. Patent and Trademark Office has issued more than 4,400 patents for mouse traps over the years, I’ve never found one that works satisfactorily. Most are difficult to bait, and I’ve had my fingers snapped more times than I care to remember.

Quick-Kill traps

But last fall I found what has proven to be a truly better mouse trap. Victor Quick-Kill Mouse Traps (www.victorpest.com) are easy to bait, set, and empty. The trap’s powerful spring and kill bar work quickly, efficiently, and humanely, especially when baited with peanut butter. If you have a mouse problem, find these traps at the web site or at hardware stores, garden centers, and big box stores.

Price varies, but expect to pay between two and three dollars per trap.