Shrews are a very, very strange group of animals. I will do a post on shrews in general in the future, just because there are many odd facts about them. But today I’d like to focus on one particular shrew. The northern short-tailed shrew has the distinction of being of being one of the few venomous mammals in the world.
There are three confirmed species of venomous shrews: the northern short-tail, the Mediterranean water shrew, and the Eurasian water shrew. I’m going to write about the short-tailed shrew, because it lives in North America, and I had no idea a venomous mammal lives so close to me. Northern short-tails range from Saskatchewan to the Atlantic coast, and down to Georgia and Nebraska in the south. They are very adaptable animals, living in a variety of habitats from woodlands to bogs to fields and gardens.
Short-tailed shrews grow to be between 7.5 cm and 10.5 cm long, with tail length between one and three centimetres. Males are slightly bigger than females, but otherwise there is little sexual dimorphism. Northern short-tailed shrews have pretty, velvety grey fur, which lightens slightly in the summer. They have short snouts (for shrews) and tiny ears that can’t be seen through the shrews’ fur.
All shrews have incredible appetites, and the northern short-tail is no exception. These little guys can eat three times their body weight each day. Though they mostly eat insects, these shrews will also eat small animals, including snakes, frogs, mice, birds, and other shrews. There are two theories as to why short-tails possess venom. The first is that the venom allows the shrews to store their prey in a comatose state, thus providing them with ready meals in harsh times. Another argument suggests that the venom allows shrews to capture larger prey than they would otherwise be able to tackle. It’s probably a bit of both.
As nocturnal and semi-fossorial (burrowing) animals, shrews have little need of a developed sense of sight. Instead, they use their whiskers and snout to feel their way around, as well as using echolocation to navigate. They are also believed to have a poor sense of smell, which makes the distinctive odour they cover themselves in all the more perplexing. One thought is that this smelly substance (which also tastes nasty) is a deterrent to any predator that might think a shrew would make a good meal.
Reproduction in northern short-tailed shrews occurs at an impressive rate. Gestation lasts just over three weeks, with the female giving birth to six to eight young per litter. She doesn’t spend much time with them, as they are weaned after only 25 days. The mother can then go on to have more litters, sometimes having three in a single year. The young mature extraordinarily quickly, reaching sexual maturity in two to three months. Those born early in the year will sometimes have a litter of their own in the same breeding season as when they were born.
As you might imagine with such an explosive reproductive rate, northern short-tailed shrews are very common and are doing quite well. Though many don’t survive until adulthood, I think they compensate for this by popping out as many babies as they can. Not a bad strategy, it seems!