b. brevicauda subspecies appeared later. Range This shrew is found throughout central and eastern North America, from southern Saskatchewan to Atlantic Canada and south to northern Arkansas and Georgia. It is probably the most common shrew in the Great Lakes region. Population densities usually range from five to 30 shrews per hectare (two to 12 per acre), but rarely exceed 200/ha (80/ac). The typical home range of a shrew is 2.5 ha, and may overlap slightly with the ranges of other shrews. Habitat Both disturbed and undisturbed habitats are used by the northern short-tailed shrew, including grasslands, old fields, fencerows, marshy areas, deciduous and coniferous forests, and household gardens, though the preferred habitats are those which are moist with leaf litter or thick plant cover. Burned-over forests are not quickly recolonized by B. brevicauda, and shrews quickly depart clear-cuts. Diet This shrew consumes up to three times its weight in food each day. It eats small quantities of subterranean fungi and seeds, though it is mostly carnivorous. It prefers insects, earthworms, voles, snails, and other shrews for the bulk of its diet, though salamanders and mice are also eaten. This shrew consumes vertebrates more often than other shrews do. The shrew mostly forages within a few hours after sunset, though it is also active during cloudy days. High evaporative water loss requires the shrew to have access to a source of water, though it does obtain water from its food, as well. The shrew often hoards food, especially in the fall and winter, or during a time of prey abundance; one study found it caches 87% of the prey it catches, while 9% is eaten immediately and 4% is left where it was killed. Toxin The saliva of the northern short-tailed shrew contains a kallikrein-like protease, used to paralyze and subdue its prey. The toxin is strong enough to kill small animals, up to sizes somewhat larger than the shrew itself, and results in painful bites to humans who attempt to handle the shrew. The venomous saliva is secreted from submaxillary glands, through a duct which opens at the base of the lower incisors, where the saliva flows along the groove formed by the two incisors, and into the prey. The toxin is very similar in structure to the one produced by the Mexican beaded lizard (Heloderma horridum) which independently developed its toxin from the same precursor protein. Physiology Senses