The Northern short-tailed shrew, Blarina brevicauda, is a mammal found across North America. This small creature is frequently mistaken for a rodent, though it belongs to the order Eulipotyphla, making it more closely related to moles and hedgehogs than to mice. It is one of the most common shrews across its range, yet its secretive, subterranean lifestyle means it rarely encounters humans. The shrew is active both day and night.
Physical Characteristics and Habitat
The Northern short-tailed shrew is a robust, mouse-sized mammal, measuring between 108 to 140 millimeters (4.3 to 5.5 inches) in total length, with a short tail ranging from 18 to 32 millimeters (0.7 to 1.3 inches). Its body is stocky, covered in dense, velvety fur that appears uniformly slate gray, sometimes with slightly paler underparts. The shrew’s pointed snout is relatively short and heavy compared to other shrews, and its tiny eyes and ears are almost entirely hidden by its fur.
This species inhabits a wide geographic area across east-central North America, extending from southern Saskatchewan and Nova Scotia in Canada down to central Nebraska and Georgia in the United States. Northern short-tailed shrews can be found in nearly all terrestrial habitats, but they are most abundant in damp, brushy woodlands, bogs, marshes, and the weedy borders of fields. They prefer environments with deep leaf litter or loose soil, which allows them to construct runways and nests underground or under logs and rocks.
Diet and High Metabolism
The Northern short-tailed shrew has a largely carnivorous diet, consuming invertebrates and small vertebrates. Its prey includes earthworms, snails, slugs, insect larvae, millipedes, spiders, mice, voles, salamanders, frogs, and snakes. This appetite is driven by a high metabolic rate, requiring the shrew to consume three times its own body weight in food daily.
To manage larger prey, the shrew uses its specialized saliva. It stores surplus food, such as snails and beetles, for later consumption. This behavior is linked to its need for continuous energy, as it does not hibernate and remains active year-round. The high demand for energy means the shrew is constantly foraging or resting in short bursts to process its meals.
The Venomous Bite
The Northern short-tailed shrew is one of the few venomous mammals in the world. Its toxic saliva, known to contain blarina toxin (BLTX), is produced in specialized submaxillary and sublingual glands located in its lower jaw. This venom is then delivered to its prey through grooves in its lower incisors during a bite.
The primary purpose of this venom is to paralyze prey, rather than to cause immediate death. This allows the shrew to subdue larger animals, such as mice or voles, and then store them alive but immobilized in its burrow for future consumption. For humans, a bite from a Northern short-tailed shrew can cause a local burning sensation around the puncture marks, followed by localized swelling. While painful, the effects are not life-threatening and subside within a few days.
Sensory Abilities and Lifespan
Northern short-tailed shrews have poor eyesight, distinguishing between light and dark. To compensate, they rely on other developed senses. They have a keen sense of touch, particularly through their pointed snout and whiskers (vibrissae), which helps them navigate their dark environment.
These shrews use echolocation, similar to bats and dolphins, to perceive their surroundings and locate prey. They emit ultrasonic clicks and interpret the returning echoes to understand their environment. This sensory adaptation allows them to hunt and move through underground tunnel systems and dense leaf litter. Northern short-tailed shrews have a short lifespan in the wild, ranging from 1 to 3 years. Females produce multiple litters per year, typically two or three, with gestation lasting 21 to 22 days and litter sizes ranging from 3 to 10 young.