A shrew is a small, mole-like mammal often mistaken for a mouse due to its size. Despite this common confusion, the shrew is neither a herbivore nor a rodent. This tiny animal is classified as an insectivore and an opportunistic carnivore. Its anatomy, from its teeth to its metabolism, is adapted for a high-protein diet, making the consumption of plant matter secondary and rare.
Shrews Are Strictly Insectivorous
The diet of a shrew is dominated by invertebrates, which is why it is classified primarily as an insectivore. They actively hunt and consume a variety of prey, including earthworms, spiders, slugs, snails, and the larvae and adults of many insects like beetles and moths. This specialized, high-protein intake is necessary for their survival and reflects their predatory nature.
Shrews are not limited to insects and will opportunistically prey on small vertebrates, such as baby mice, voles, and lizards. Their dentition is perfectly adapted for this carnivorous lifestyle, featuring sharp, spike-like teeth designed for tearing flesh and crushing hard exoskeletons. Some shrew species exhibit a reddish pigment in their teeth, caused by iron deposits, which increases the enamel’s wear resistance. This adaptation helps prolong the life of their single set of adult teeth.
The High-Energy Demands of Shrew Metabolism
The physiological reason a shrew cannot subsist on a herbivorous diet is rooted in its exceptionally high basal metabolic rate (BMR). This tiny mammal expends energy at a frantic pace, requiring a constant and dense source of calories to maintain its body temperature and activity. A shrew’s heart rate can exceed 1,200 beats per minute, which is indicative of its demanding internal engine.
Because of this rapid metabolism, a shrew must consume an immense amount of food relative to its body weight every day, often eating 80% to 100% of its mass within a 24-hour period. Going without food for even a few consecutive hours can be fatal for some species. To sustain this frantic pace, shrews have evolved to be highly effective hunters, with some species possessing venomous saliva to quickly subdue prey larger than themselves, such as small rodents or frogs.
When food becomes scarce, shrews have a survival mechanism known as torpor, which is similar to a short-term hibernation. This state allows them to temporarily lower their body temperature and metabolic rate, conserving energy until better foraging conditions return. The constant, high-caloric need created by their BMR dictates that their diet must be protein-rich and easily digestible, which excludes the majority of fibrous plant matter.
Why Shrews Are Not Rodents or Herbivores
The common misconception that the shrew is a herbivore stems from its superficial resemblance to mice and voles, which are rodents and often plant-eaters. Shrews belong to the order Eulipotyphla, a group that includes moles and hedgehogs, and are not members of the order Rodentia.
The most telling difference between a shrew and a rodent is found in the teeth. Rodents possess large, chisel-shaped incisors that grow continuously and are used for gnawing plant materials. Shrews, conversely, have sharp, non-growing, spike-like teeth suited for capturing and dissecting animal prey.
Furthermore, the digestive system of a shrew is designed for the rapid processing of animal protein. Unlike herbivores, they lack specialized adaptations, such as large cecums or complex stomachs, necessary to break down the tough cellulose found in plant matter. Plant material is only consumed incidentally or in times of extreme hunger, serving little nutritional purpose for the shrew’s demanding metabolism.