The shrew is a tiny, long-snouted mammal belonging to the order Eulipotyphla, not the order Rodentia (mice and voles). Although they resemble mice, shrews are more closely related to moles and hedgehogs. They possess sharp, spike-like teeth instead of the gnawing incisors typical of rodents. Shrews are highly specialized, high-energy insectivores constantly hunting prey to fuel their existence.
The Primary Insectivorous Diet
Shrews are classified as insectivores because their primary diet consists of invertebrates. They forage constantly in leaf litter and soil for prey such as earthworms, insect larvae, slugs, and snails. They also consume numerous insects like beetles, grasshoppers, centipedes, and spiders, using their sharp teeth to break down hard exoskeletons. The shrew’s diet is not strictly limited to invertebrates, however. Larger species, such as some short-tailed shrews, are opportunistic predators that may prey on small vertebrates like mice, nestling birds, or small snakes when invertebrate food sources are scarce.
High Metabolism and Constant Foraging
The shrew’s tiny size results in an exceptionally high surface area to volume ratio, causing rapid heat loss and necessitating an extremely high metabolic rate. This intense physiological demand requires shrews to consume vast quantities of food simply to survive. Many species must eat the equivalent of 80% to 100% of their body weight daily. Shrews cannot afford to fast for more than a few hours, forcing them to forage almost continuously day and night and preventing them from entering hibernation.
Specialized Hunting Adaptations
To sustain their high energy demands, shrews rely on specific adaptations for locating and subduing prey. Since their eyesight is poor, they rely heavily on keen senses of smell and touch, using their long snouts and sensitive whiskers to detect movement under the soil or in the dark. Some species, such as the Northern Short-tailed Shrew, possess an adaptation unique among mammals: paralytic venom delivered through grooves in their lower incisor teeth. This venom subdues and immobilizes larger prey, allowing the shrew to cache it as a “live larder” for later consumption. Certain species also utilize high-frequency ultrasonic squeaks, or “echolocation,” for spatial orientation and habitat assessment.
Role in the Ecosystem
The shrew’s constant foraging activity places it in an important position within its ecosystem. By consuming large quantities of insects, larvae, and slugs, shrews function as natural pest controllers, limiting populations detrimental to agriculture and gardens. Their intense predation helps maintain the balance of invertebrate communities in the soil and leaf litter. Despite possessing noxious scent glands that deter many mammalian predators, shrews still serve as a food source for numerous animals, including owls, hawks, and snakes. This ensures the energy gained from their insectivorous diet is cycled back into the food chain.