Mammals range from the blue whale to species weighing less than a paperclip. A mammal is defined as a warm-blooded vertebrate that possesses mammary glands to produce milk and has hair or fur. Determining the smallest mammal requires clarifying whether measurement is by body mass or body length. The Etruscan Shrew, Suncus etruscus, is the consensus smallest mammal by weight, though another species competes based on physical length.
The Etruscan Shrew
The Etruscan Shrew holds the title as the smallest mammal by mass, typically weighing between 1.3 and 2.5 grams, averaging about 1.8 grams. Its body length ranges from 3 to 5.2 centimeters, with the tail adding another 2.4 to 3.2 centimeters.
This tiny insectivore has a slender body, a large head, and a long, mobile snout (proboscis) used for sensing and hunting. Its fur is generally soft, pale brown or gray, and lighter underneath. The Shrew is widely distributed from Europe and North Africa, through the Middle East, and as far east as Malaysia.
These shrews prefer warm, damp habitats with plenty of ground cover, such as Mediterranean scrublands or riparian thickets. They utilize rock crevices, stone walls, or tunnels abandoned by other animals for shelter, as they do not typically dig their own burrows. Their exceptional sense of touch, supported by prominent whiskers, compensates for poor eyesight, allowing them to navigate and hunt effectively.
The Biological Price of Being Tiny
The shrew’s miniature size creates extreme biological challenges due to its surface area-to-volume ratio. Because a smaller body has a larger surface area relative to its volume, the Etruscan Shrew loses body heat rapidly. To counteract this constant heat loss and maintain a stable internal temperature, the shrew requires an exceptionally high metabolic rate.
This pace necessitates a constant, high caloric intake, driving the shrew to consume food amounting to 1.5 to 2 times its body weight daily. Without this continuous fuel supply, the animal can starve to death in just a few hours. The Etruscan Shrew’s heart beats at an astonishing rate, reaching up to 1,511 beats per minute (approximately 25 beats per second).
To survive periods when food is scarce, such as during cold snaps, the shrew employs a survival strategy called torpor. During torpor, the animal significantly lowers its body temperature and metabolic rate, temporarily reducing energy expenditure. This adaptation allows the species to persist in fluctuating environments.
Other Miniature Mammals
While the Etruscan Shrew is the lightest mammal, the Kitti’s Hog-Nosed Bat, Craseonycteris thonglongyai, often competes for the title. Also known as the Bumblebee Bat, this species is cited as the smallest mammal by length and skull size. Its head and body measure only 29 to 33 millimeters, making it shorter than the shrew, though it weighs a comparable average of about 2 grams.
The comparison between the Shrew (lighter) and the Bat (shorter) highlights the difficulty in defining the single “smallest” mammal. Beyond these two primary contenders, other mammals demonstrate extreme miniaturization within their specific groups.
Other Examples of Miniaturization
The Long-Tailed Planigale, a carnivorous marsupial from Australia, is one of the smallest marsupials. It is known for its flat head, which allows it to slip into soil cracks while hunting. Madame Berthe’s Mouse Lemur, Microcebus berthae, holds the record as the smallest primate species. Found only in Madagascar, this lemur has an average body mass of about 30 grams. These miniature mammals demonstrate the diverse ways life has adapted to thrive at the lower bounds of mammalian size.