The Etruscan shrew, known scientifically as Suncus etruscus, holds the title of the smallest known mammal in the world by mass. This tiny creature is a subject of fascination due to its extreme size, which dictates much of its biology and behavior.
Precise Measurements of the Etruscan Shrew
The Etruscan shrew is small, with a body length that ranges from 36 to 53 millimeters, not including its tail. The tail itself adds another 21 to 30 millimeters to its total length. What truly defines its status is its minuscule mass, which typically averages around 2 grams, though it can range from 1.3 to 2.5 grams. To support its energetic lifestyle, its brain is the largest in the animal kingdom in proportion to its body weight.
This animal’s physical characteristics are as distinct as its size. It has a slender body, a large head relative to its body, and a long, mobile snout. The shrew’s ears are also relatively large and noticeable.
Contextualizing Its Size
Weighing around two grams, the Etruscan shrew is lighter than a U.S. dime and has about the same mass as two dollar bills. Its body is shorter than the average human thumb. This diminutive stature often leads to comparisons with another tiny mammal, the bumblebee bat, for the title of the world’s smallest.
The distinction between the two is a matter of metrics. The Etruscan shrew is the smallest mammal when measured by mass. The bumblebee bat, however, is often considered the smallest based on its skull size and body length, which is just over an inch. Therefore, while the bat may be shorter, the shrew weighs less, securing its title as the lightest mammal on Earth.
Biological Consequences of Small Stature
The Etruscan shrew’s tiny body has significant biological implications, primarily related to its metabolism. Due to its high surface-area-to-volume ratio, it loses body heat at a very rapid pace. This constant heat loss requires an extremely fast metabolism to maintain a stable body temperature. As a result, the shrew must consume 1.5 to 2 times its own body weight in food each day.
This intense metabolic rate is supported by a heart that beats at incredible speeds. An Etruscan shrew’s heart can reach up to 1,500 beats per minute, which is about 25 beats per second. During periods of cold or food scarcity, the shrew can enter a state of temporary hibernation called torpor, lowering its body temperature to conserve energy.