Although its external appearance is generally that of a long-nosedmouse, a shrew is not arodent, as mice are. It is, in fact, a much closer relative ofhedgehogs and moles; shrews are related to rodents only in that both belong to theBoreoeutheriamagnorder. Shrews have sharp, spike-like teeth, whereas rodents have gnawing front incisor teeth.
The shrew family has 385 known species, making it the fourth-most species-diverse mammal family. The only mammal families with more species are themuroid rodent families (Muridae andCricetidae) and thebat familyVespertilionidae.
All shrews are tiny, most no larger than a mouse. The largest species is theAsian house shrew (Suncus murinus) of tropical Asia, which is about 15 cm (6 in) long and weighs around 100 g (3+1⁄2 oz)[2] TheEtruscan shrew (Suncus etruscus), at about3.5 cm (1+3⁄8 in) and 1.8 grams (28 grains), is the smallest known living terrestrial mammal.
Water shrew skeleton
In general, shrews are terrestrial creatures that forage for seeds, insects, nuts, worms, and a variety of other foods inleaf litter and dense vegetation e.g.grass, but some specialise in climbing trees, living underground, livingunder snow, or even hunting in water. They have small eyes and generally poorvision, but have excellent senses ofhearing andsmell.[3] They are very active animals, with voracious appetites. Shrews have unusually highmetabolic rates, above that expected in comparable small mammals.[4] For this reason, they need to eat almost constantly likemoles. Shrews in captivity can eat1⁄2 to 2 times their own body weight in food daily.[5]
They do nothibernate, but some species are capable of enteringtorpor. In winter, many species undergomorphological changes that drastically reduce their body weight. Shrews can lose between 30% and 50% of their body weight, shrinking the size of bones, skull, and internal organs.[6]
Whereas rodents have gnawingincisors that grow throughout life, the teeth of shrews wear down throughout life, a problem made more extreme because they lose theirmilk teeth before birth, so have only one set of teeth throughout their lifetimes. In some species, exposed areas of the teeth contain iron and are dark red. The iron reinforces the surfaces that are exposed to the most stress, which helps prolong the life of the teeth. This adaptation is not found in species with lower metabolism, which do not have to eat as much and therefore do not wear down the enamel to the same degree. The only other mammals' teeth with pigmented enamel are the incisors of rodents.[7] Apart from the first pair of incisors, which are long and sharp, and the chewingmolars at the back of the mouth, the teeth of shrews are small and peg-like, and may be reduced in number. Thedental formula of shrews is:3.1.1-3.31-2.0-1.1.3
Shrews are fiercely territorial, driving off rivals, and coming together only to mate. Many species digburrows for catching food and hiding frompredators, although this is not universal.[3]
Female shrews can have up to 10 litters a year; in the tropics, they breed all year round; in temperate zones, they cease breeding only in the winter. Shrews havegestation periods of 17–32 days. The female often becomes pregnant within a day or so of giving birth, andlactates during her pregnancy,weaning one litter as the next is born.[3] Shrews live 12 to 30 months.[8]
A characteristic behaviour observed in many species of shrew is known as "caravanning". This is when a litter of young shrews form a line behind the mother, each gripping the shrew in front by the fur at the base of the tail.[9]
Shrews are unusual among mammals in a number of respects. Unlike most mammals, some species of shrews arevenomous. Shrew venom is not conducted into the wound byfangs, but by grooves in the teeth. The venom contains various compounds, and the contents of the venom glands of theAmerican short-tailed shrew are sufficient to kill 200 mice by intravenous injection. One chemical extracted from shrew venom may be potentially useful in the treatment of high blood pressure, while another compound may be useful in the treatment of someneuromuscular diseases andmigraines.[10][better source needed] The saliva of thenorthern short-tailed shrew (Blarina brevicauda) containssoricidin, apeptide which has been studied for use in treatingovarian cancer.[11] Also, along with thebats andtoothed whales, some species of shrews useecholocation.[12] Unlike most other mammals, shrews lackzygomatic bones (also called thejugals), so have incompletezygomatic arches.[13]
The only terrestrial mammals known toecholocate are two genera (Sorex andBlarina) of shrews, thetenrecs ofMadagascar,bats, and thesolenodons.[14] These include theEurasian or common shrew (Sorex araneus) and the Americanvagrant shrew (Sorex vagrans) andnorthern short-tailed shrew (Blarina brevicauda). These shrews emit series of ultrasonic squeaks.[15][16] By nature the shrew sounds, unlike those of bats, are low-amplitude, broadband, multiharmonic, and frequency modulated.[16] They contain no "echolocation clicks" withreverberations and would seem to be used for simple, close-range spatial orientation. In contrast to bats, shrews use echolocation only to investigate their habitats rather than additionally to pinpoint food.[16]
Except for large and thus strongly reflecting objects, such as a big stone or tree trunk, they probably are not able to disentangle echo scenes, but rather derive information on habitat type from the overall call reverberations. This might be comparable to human hearing whether one calls into a beech forest or into a reverberant wine cellar.[16]
The 385 shrew species are placed in 26 genera,[17] which are grouped into three living subfamilies: Crocidurinae (white-toothed shrews),Myosoricinae (African shrews), and Soricinae (red-toothed shrews). In addition, the family contains the extinct subfamiliesLimnoecinae,Crocidosoricinae,Allosoricinae, andHeterosoricinae (although Heterosoricinae is also commonly considered a separate family). A new genus was tentatively erected,Nagasorex along with the description of a new species,[18] but as of 2025[update] this genus and species status has not been confirmed.
^Louch CD, Ghosh AK, Pal BC (1966). "Seasonal Changes in Weight and Reproductive Activity of Suncus murinus in West Bengal, India".Journal of Mammalogy.47 (1):73–78.doi:10.2307/1378070.JSTOR1378070.PMID5905563.
Forsman KA, Malmquist MG (1988). "Evidence for echolocation in the common shrew,Sorex araneus".Journal of Zoology.216 (4):655–662.doi:10.1111/j.1469-7998.1988.tb02463.x.
Hutterer R (1976).Deskriptive und vergleichende Verhaltensstudien an der Zwergspitzmaus,Sorex minutus L., und der Waldspitzmaus,Sorex araneus L. (Soricidae - Insectivora - Mammalia) (Ph.D. Thesis) (in German). Univ. Wien.OCLC716064334.
Irwin DV, Baxter RM (1980). "Evidence against the use of echolocation byCrocidura f. flavescens (Soricidae)".Säugetierkundliche Mitteilungen.28 (4): 323.
Kahmann H, Ostermann K (July 1951). "[Perception of production of high tones by small mammals]" [Perception of production of high tones by small mammals].Experientia (in German).7 (7):268–9.doi:10.1007/BF02154548.PMID14860152.S2CID26738585.
Köhler D, Wallschläger D (1987). "Über die Lautäußerungen der Wasserspitzmaus,Neomys fodiens (Insectivora: Soricidae)" [On vocalization of the european water shrew Neomys fodiens (Insectivora: Soricidae)].Zoologische Jahrbücher (in German).91 (1):89–99.
Sales G, Pye D (1974).Ultrasonic communication by animals. London.{{cite book}}: CS1 maint: location missing publisher (link)
