A shrew or shrew mouse is a small mole-like mammal classified in the order Soricomorpha.
True shrews are also not to be confused with West Indies shrews, treeshrews, otter shrews,
or elephant shrews, which belong to different families or orders.
Although its external appearance is generally that of a long-nosed mouse, a shrew is not
a rodent, as mice are, and is in fact more closely related to moles. Shrews have sharp,
spike-like teeth, not the familiar gnawing front incisor teeth of rodents.
Shrews are distributed almost worldwide: of the major tropical and temperate land masses,
only New Guinea, Australia, and New Zealand do not have any native shrews; in South America,
shrews are relatively recent immigrants and are present only in the northern Andes. In
terms of species diversity, the shrew family is the fourth most successful mammal family,
being rivalled only by the muroid rodent families Muridae and Cricetidae and the bat family
Vespertilionidae.
Characteristics All shrews are comparatively small, most no
larger than a mouse. The largest species is the Asian house shrew of tropical Asia, which
is about 15 cm long and weighs around 100 grams; several are very small, notably the Etruscan
shrew, which at about 3.5 cm and 2 grams is the smallest living terrestrial mammal.
In general, shrews are terrestrial creatures that forage for seeds, insects, nuts, worms
and a variety of other foods in leaf litter and dense vegetation, but some specialise
in climbing trees, living underground, living under snow or even hunting in water. They
have small eyes, and generally poor vision, but have excellent senses of hearing and smell.
They are very active animals, with voracious appetites. Shrews have an unusually high metabolic
rate, above that expected in comparable small mammals. Shrews typically eat 80–90% of
their own body weight in food daily. They do not hibernate, but are capable of
entering torpor. In winter, many species undergo morphological 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. Whereas rodents have gnawing incisors that
grow throughout life, the teeth of shrews wear down throughout life, a problem made
more extreme because they lose their milk teeth before birth, and therefore have only
one set of teeth throughout their lifetimes. Apart from the first pair of incisors, which
are long and sharp, and the chewing molars at the back of the mouth, the teeth of shrews
are small and peg-like, and may be reduced in number. The dental formula of shrews is:3.1.1-3.31-2.0-1.1.3
Shrews are fiercely territorial, driving off rivals, and only coming together to mate.
Many species dig burrows for caching food and hiding from predators, although this is
not universal. Female shrews can have up to 10 litters a
year; in the tropics, they breed all year round; in temperate zones, they only stop
breeding in the winter. Shrews have gestation periods of 17–32 days. The female often
becomes pregnant within a day or so of giving birth, and lactates during her pregnancy,
weaning one litter as the next is born. Shrews live 12 to 30 months.
Shrews are unusual among mammals in a number of respects. Unlike most mammals, some species
of shrew are venomous. Shrew venom is not conducted into the wound by fangs, but by
grooves in the teeth. The venom contains various compounds, and the contents of the venom glands
of the American 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 some neuromuscular
diseases and migraines. The saliva of the northern short-tailed shrew contains the peptide
soricidin, which has been studied for use in treating ovarian cancer. Also, along with
the bats and toothed whales, some species of shrews use echolocation. Unlike most other
mammals, shrews lack zygomatic bones, so have incomplete zygomatic arches.
Echolocation
The only terrestrial mammals known to echolocate are two genera of shrews and the tenrecs of
Madagascar. These include the vagrant shrew, the common or Eurasian shrew, and the northern
short-tailed shrew. The shrews emit series of ultrasonic squeaks. The nature of shrew
sounds, unlike those of bats, are low amplitude, broadband, multiharmonic and frequency modulated.
They contain no "echolocation clicks" with reverberations 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.
Except for large and thus strongly reflecting objects, such as a big stone or tree trunk,
they will probably not be 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.
Classification The 385 shrew species are in 26 genera, which
are grouped into three living subfamilies: Crocidurinae, Myosoricinae and Soricinae.
In addition, the family contains the extinct subfamilies Limnoecinae, Crocidosoricinae,
Allosoricinae and Heterosoricinae. Family Soricidae
Subfamily Crocidurinae Crocidura
Diplomesodon Feroculus
Paracrocidura Ruwenzorisorex
Scutisorex Solisorex
Suncus Sylvisorex
Subfamily Myosoricinae Congosorex
Myosorex Surdisorex
Subfamily Soricinae Tribe Anourosoricini
Anourosorex
Tribe Blarinellini Blarinella
Tribe Blarinini Blarina
Cryptotis
Tribe Nectogalini Chimarrogale
Chodsigoa Episoriculus
Nectogale Neomys
†Nesiotites Soriculus
Tribe Notiosoricini Megasorex
Notiosorex
Tribe Soricini Sorex
References
Further reading Buchler, E.R. 1973. The use of echolocation
by the wandering shrew, Sorex vagrans Baird. Diss. Abstr. Int. B. Sci. Eng. 33(7): 3380–3381.
Buchler, E.. "The use of echolocation by the wandering shrew". Animal Behaviour 24: 858–873.
doi:10.1016/S0003-3472(76)80016-4. Busnel, R.-G.. 1963. Acoustic Behaviour of
Animals. Amsterdam: Elsevier Publishing Company. Forsman, K. A.; Malmquist, M. G.. "Evidence
for echolocation in the common shrew,Sorex araneus". Journal of Zoology 216: 655. doi:10.1111/j.1469-7998.1988.tb02463.x.
Gould, E. 1962. Evidence for echolocation in shrews.Ph.D. Thesis, Tulane University.
Gould, E.; Negus, N. C.; Novick, A.. "Evidence for echolocation in shrews". Journal of Experimental
Zoology 156: 19–37. doi:10.1002/jez.1401560103. PMID 14189919.
Hutterer, Rainer. Deskriptive und vergleichende Verhaltensstudien an der Zwergspitzmaus, Sorex
minutus L., und der Waldspitzmaus, Sorex araneus L.. Univ. Wien. OCLC 716064334.
Hutterer, Rainer; Vogel, Peter. "Abwehrlaute afrikanischer Spitzmäuse der Gattung Crocidura
Wagler, 1832 und ihre systematische Bedeutung". Bonn. Zool. Beitr 28: 218–27.
Hutterer, R.; Vogel, P.; Frey, H.; Genoud, M.. "Vocalization of the
shrews Suncus etruscus and Crocidura russula during normothermia and torpor". Acta Theriologica
24: 267–71. Irwin, D.V., Baxter, R.M. 1980. Evidence against
the use of echolocation by Crocidura f. flavescens. Säugetierk. Mitt. 28(4): 323.
Kahmann, H.; Ostermann, K.. "Wahrnehmen und Hervorbringen hoher Töne bei kleinen Säugetieren"
[Perception of production of high tones by small mammals]. Experientia 7: 268–269.
doi:10.1007/BF02154548. PMID 14860152. Köhler, D.; Wallschläger, D.. "Über die
Lautäußerungen der Wasserspitzmaus, Neomys fodiens" [On vocalization of the european
water shrew Neomys fodiens]. Zoologische Jahrbücher 91: 89–99.
Sales, G., Pye, D. 1974. Ultrasonic communication by animals. London.