Nature Note: Shrews

Posted by: Tony Mills

Tagged in: nature notes , mammals

The Biting of the Shrew

I felt a sting on the tip of my finger and at first I could not figure out what had poked, bitten or stung me. Closer inspection revealed a small silvery mammal racing around the bottom of the  drift fence bucket ( a pitfall trap used for animal surveys). I quickly realized that a shrew had latched on to me, presumably to protect itself. It took a minute to sink in; I had actually been bitten by one of only a couple of venomous mammals in the whole world. My finger turned red on the end and ached mildly for a few days but it was totally worth it!

Many people don’t realize that our yards and woods are home to miniscule venomous mammals called shrews. Shrews belong to a family of small mammals called insectivores. This large family also includes moles and hedgehogs. One member of the shrew family, the Etruscan shrew, has the distinction of being the world’s smallest mammal. It weighs only about two grams (less than a penny). The much larger short-tailed shrew (about half the size of a mouse) is a common resident of vacant lots and wooded areas in the lowcountry. There is a good chance that your cat or dog has excavated a shrew tunnel and left the carcass on your doorstep. Shrews secrete a musky odor and apparently have a foul taste so they are often killed but rarely eaten by domestic pets.

Don’t let the short-tailed shrew’s small size fool you. These tiny insectivores are voracious predators, attacking animals much larger than themselves and subduing them with toxic saliva. Venom is the shrew’s meal ticket, allowing it to immobilize insects, worms, frogs, salamanders and small mammals for eating. Shrews often find food using echolocation, a similar system to that used by bats. They send out a series of clicks and chirps through underground tunnels and listen for returning echoes that allow them to differentiate between food and non-edible material. Some shrews will capture and ingest two to three times their body weight in a single day. Shrews owe their insatiable appetites to their spectacular metabolisms. A short-tailed shrew’s resting heart rate can be 800 beats per minute and a relaxing shrew may breathe 168 times in 60 seconds. Shrews often prepare for lean times by caching a selection of snails, worms and beetles and even small snakes to insure ample food supplies for the winter.

Short-tailed shrews mate in any season and females often have three or more litters of 5-7 pups per year. The young shrews are weaned and leave the nest within a month of birth. They may live as long as three years but usually don’t survive past the first. Shrews are intolerant of each other, except during breeding, and will fight and even kill each other in territorial disputes.

Because shrews are very abundant and eat large quantities of invertebrates they are considered beneficial. They feed on a variety of harmful insect species like mole crickets and other pests. It is very unlikely that a person would be harmed by a shrew unless they tried to pick it up. So, while it was pretty silly for me to put my hand in a pitfall trap before looking inside, I feel kind of lucky to have been bitten by the only venomous mammal in this hemisphere.

-tony