Not every critter that's stirring in your home is a mouse or even a rodent. One small creature that may invade your space is the North American Pygmy shrew. Overall, this mammal is a beneficial and highly skilled predator that kills damaging pests and lives a high-energy lifestyle. 

Learn to tell a shrew apart from a mouse with a few key indicators. Your small, warm invader is a shrew if it exhibits the following characteristics:

Smells musty

Many shrew infestations are discovered after a musty smell appears in the building or home. Some speculate that the scent—released by male shrews—is a mate attractant, while other researchers believe that the pungent secretions taste terrible to deter predators who try to eat shrews. (That's the reason why your cat won't eat them perhaps.) Either way, their funky stink often gives shrews away.

Eats a lot of insects

Shrews never hibernate. They don't have time for that drowsy nonsense. They're too busy eating up to three times their body weight in insects, small mice, and spiders per day. They eat more in the winter to keep themselves warm.

Is less than four inches long

Shrews are tiny little things from two to four inches in length. They don't even weigh an ounce. If you're noticing fat little vermin scrambling around, and they're larger than four inches long, you don't have shrews.

Climbs and burrows

Shrews love to create little burrows and tunnels to get from place to place and stay warm en route. They may take over old mouse and rodent burrows. They usually live solitary lives, and they have been also seen climbing a small way up trees and posts to reach bird feeders and other food sources.

Is mostly nocturnal

Shrews are active round-the-clock because of their super-sonic metabolism, but they're more active at night. Since they're timid creatures, they may be more active in your home when you're asleep. They're really afraid of loud noises and sudden surprises.

Is sometimes vocal

Shrews get their name from being naggers who make a lot of noise. Some of the sounds they emit are at ultrasonic frequencies humans can't hear. They also emit clicks, chirps, and buzzing when mating or when getting territorial.

Has a painful bite

The bite of the North American Pygmy shrew is venomous but not normally life-threatening. It will sting like the dickens for a few days, so be sure to wear gloves or other protection when going shrew hunting.

Enjoys water

Some shrew are great swimmers, and all shrews in North America enjoy living in moist environments. Their high metabolism creates an increased need for moisture when it's warm and dry outside. If you suspect you have shrews, check around pooling water, poorly draining flower beds, and other moist areas. Shrews dry out quickly and will move on if you remove humid areas that are sources of life-sustaining water and juicy insect meals.

For more tips on how to spot and remove pests, work with a company like Greenleaf Organic Pest Management.