Living Sanibel: The untamed shrews
Southern Short-tailed Shrew
Roughly the same size as a house mouse, this small member of the Soricomorhpa family is not a rodent (Rodentia). Worldwide there are 246 known species in 22 genera, with distribution on every continent excepting Australia and Antarctica. Southwest Florida is home to two species: the southern short-tailed shrew and the smaller least shrew. A subspecies, called Sherman’s short-tailed shrew, was once found exclusively in Lee County, though it is now believed to be extinct.
The shrew is easy to distinguish from the similar-looking house or field mouse by its distinctive long, pointed snout. It is a fascinating creature because of its tiny size, venomous bite, and unusual metabolism.
The shrew’s heart rate is close to 1,000 beats per minute. A normal human heart rate is 60 beats per minute, or 16 times slower. Because of its frenetic metabolism, the shrew must eat every two hours or risk starvation. It generally consumes the equivalent of its own body weight every 24 hours.
Its bite is venomous, though the toxins produced are not at levels harmful to humans or other large mammals. The venom is injected into the prey by special grooves in the shrew’s teeth. The neurotoxins found in the shrew’s saliva rapidly lowers the blood pressure of its prey, causing the victim to have trouble breathing, slowing its heart rate, and making it easier for the tiny shrew to kill. Using this biological weapon, the shrew feeds upon much larger prey than itself, taking on rats, mice, small snakes, and reptiles. It also feeds prodigiously on insects, annelids, spiders, scorpions, mollusks, and snails. An omnivore, the shrew also eats a variety of vegetative matter.
The shrew produces two to three litters a year, with between two to six young per litter. Because its life is short and fast, a female shrew will probably have no more than four or five litters in her lifetime. It nests in burrows built in two layers, one near the surface and a deeper burrow beneath it. The shrew prefers to burrow and nest in rotting logs and other decaying vegetation. Because it is a ground-dwelling animal, the shrew is preyed upon by snakes, foxes, weasels, skunks, opossums, feral cats, and less often, owls and hawks.
The least shrew is one of the smallest mammals in the world. Only the bumblebee bat of Thailand (a.k.a. Kitti’s hog-nosed bat), weighing in at 2.5 grams (.05 ounces), rivals it for its diminutive size. Another shrew, the North American pygmy shrew, is slightly smaller, at 2.7 grams. To put it into perspective, the least shrew weighs somewhere between a penny (2.5 g.) and a quarter (5.6 g.). When you consider that within this minuscule amount of mass you have to construct a beating heart, a pair of lungs, teeth, bones, and all the muscles and internal organs that make a mammal work, it is nothing short of miraculous that members of our class (Mammalia) can be so tiny and still survive.
Like its close cousin, the southern short-tailed shrew, the least shrew is a venomous mammal. Its metabolism is also similar, requiring it to eat more than its own body weight every day to survive. The least shrew differs from the short-tailed shrew in that it is a far more social animal. It prefers living and feeding in abandoned burrows and tunnels, usually dug by moles, armadillos, or gopher tortoises. Inside these burrows groups of three to 30 least shrews will sometimes sleep together. Its nickname, bee shrew, refers to this beehive-like behavior.
The least shrew is aggressive and, using its poisonous saliva, attempts to tackle prey far larger than itself. It eats beetles, caterpillars, crickets, grasshoppers, fruit, seeds, and even carrion. It has the unique feeding technique of intentionally biting off the tail of a Cuban anole, not to catch the lizard but simply to dine on the breakaway tail. The least shrew is common prey for raccoons, skunks, snakes, hawks, owls, and foxes.
This is an excerpt from The Living Gulf Coast – A Nature Guide to Southwest Florida by Charles Sobczak. The book is available at all the Island bookstores, Baileys, Jerry’s and your favorite online sites.