Shrews
General Shrew Facts
Identification
The shrew is a small, mouse-sized
mammal with an elongated snout, a
dense fur of uniform color, small eyes,
and five clawed toes on each foot. Its skull, compared to that of
rodents, is long, narrow, and lacks the
zygomatic arch on the lateral side
characteristic of rodents. The teeth are
small, sharp, and commonly darktipped.
Pigmentation on the tips of the
teeth is caused by deposition of iron in
the outer enamel. This deposition may
increase the teeth’s resistance to wear,
an obvious advantage for permanent
teeth that do not continue to grow in
response to wear.
The house shrew
(Suncus murinus) lacks the pigmented
teeth. Shrew feces are often corkscrewshaped,
and some shrews (for example, the desert shrew [Notiosorex
crawfordi]) use regular defecation
stations. Albino shrews occur occasionally.
Shrews are similar to mice
except that mice have four toes on
their front feet, larger eyes, bicolored
fur, and lack an elongated snout.
Moles also are similar to shrews, but
are usually larger and have enlarged
front feet. Both shrews and moles are
insectivores, whereas mice are rodents.
Worldwide, over 250 species of shrews
are recognized, with over 30 species
recognized in the United States, the US
Territories, and Canada (Table 1). Specific
identification of shrews may be
difficult. Taxonomists are still refining
the phylogenetic relationships between
populations of shrews. Consult a
regional reference book on mammals,
or seek assistance from a qualified
mammalogist.
Damage Prevention and
Control Methods
Exclusion
Rodent-proof structures also exclude
shrews.
Cultural Methods
Mowing may decrease preferred
habitat and food.
Trapping
-
Mouse trap (snap trap).
- Small box trap.
- Pit trap.
Shooting
Not practical.
Other Methods
Cats may reduce densities around
structures. Owls consume large
numbers of shrews. Mowed grass
around structures may increase
predation.
Damage
Most species of shrews do not have
significant negative impacts and are
not abundant enough to be considered
pests (Schmidt 1984). Shrews sometimes
conflict with humans, however.
The vagrant shrew (Sorex vagrans) has
been reported to consume the seeds of
Douglas-fir (Pseudotsuga menziesii),
although the seeds constitute a minor
part of the diet. The masked shrew
(Sorex cinereus) destroyed from 0.3% to
10.5% of white spruce (Picea glauca)
seeds marked over a 6-year period
(Radvanyi 1970). Lodgepole pine
(Pinus contorta) seeds are also eaten by
the masked shrew. Radvanyi (1966,
1971) has published pictures of shrew,
mouse (Peromyscus, Microtus, and
Clethrionomys spp.), and chipmunk
(Eutamias spp.) damage to lodgepole
pine seeds, and describes shrew damage
to white spruce seeds.
The northern water shrew (Sorex
palustris) may cause local damage by
consuming eggs or small fish at hatcheries.
The least shrew (Cryptotis parva),
also known as the bee shrew, sometimes
enters hives and destroys the
young brood (Jackson 1961). The
northern short-tailed shrew (Blarina
brevicauda) has been reported to damage
ginseng (Panax spp.) roots.
The pugnacious nature of shrews
sometimes makes them a nuisance
when they live in or near dwellings.
Shrews occasionally fall into window
wells, attack pets, attack birds or chipmunks
at feeders, feed on stored
foods, contaminate stored foods with
feces and urine, and bite humans when
improperly handled. Potential exists
for the transmission of diseases and
parasites, but this is poorly documented.
The house shrew (Suncus murinus) is
an introduced species to Guam. It has
been reported as a host for the rat flea
(Xenopsylla cheopis) which can carry the
plague bacillus (Yersinia pestis)
(Churchfield 1990). Compared to rat
(Rattus spp.) numbers, however, house
shrew numbers are usually low, and
risk of plague transmission is probably
minimal. The house shrew is accustomed
to living around humans and
houses, which increases its damage
potential. It is considered smelly and
noisy, making incessant, shrill, clattering
sounds as it goes along (Churchfield
1990:149). On occasion it destroys
stored grain products.
Range
Shrews are broadly distributed
throughout the world and North
America. For specific range information,
refer to one of the many references
available on mammal distribution
for your region. Publications by
Burt and Grossenheider (1976), Hall
(1981), and Junge and Hoffmann
(1981) are particularly helpful.
Habitat
Shrews vary widely in habitat preferences
throughout North America.
Shrews exist in practically all terrestrial
habitats, from montane or boreal
regions to arid areas. The northern water
shrew (Sorex palustris) prefers
marshy or semiaquatic areas. Regional
reference books will help identify specific
habitats. A word of caution is in
order, however. Distribution studies
based on the results of snap-trapping
research have a pronounced tendency
to understate the abundance of
shrews. Studies using pit traps are
more successful in assessing the presence
or absence of shrews in a particular
location.
Food Habits
Shrews are in the taxonomic order
Insectivora. As the name implies,
insects make up a large portion of the
typical shrew diet. Food habit studies
have revealed that shrews eat beetles,
grasshoppers, butterfly and moth larvae,
ichneumonid wasps, crickets, spiders,
snails, earthworms, slugs,
centipedes, and millipedes. Shrews
also eat small birds, mice, small
snakes, and even other shrews when
the opportunity presents itself. Seeds,
roots, and other vegetable matter are
also eaten by some species of shrews.
General Biology,
Reproduction, and
Behavior
Shrews are among the world’s smallest
mammals. The pigmy shrew (Sorex
hoyi) is the smallest North American
mammal. It can weigh as little as 0.1
ounce (2 g). Because of their small size,
shrews have a proportionally high surface-
to-volume ratio and lose body
heat rapidly. Thus, to maintain a constant
body temperature, they have a
high metabolic rate and need to consume
food as often as every 3 to 4
hours. Some shrews will consume
three times their body weight in food
over a 24-hour period.
Shrews usually do not live longer than
1 to 2 years, but they have 1 to 3 litters
per year with 2 to 10 young per litter.
Specific demographic features vary
with the species. The gestation period
is approximately 21 days.
Shrews have an acute sense of touch,
hearing, and smell, with vision playing
a relatively minor role. Some species of
shrews use a series of high-pitched
squeaks for echolocation, much as bats
do. However, shrews probably use
echolocation more for investigating
their habitat than for searching out
food. Glands located on the hindquarters
of shrews have a pungent odor
and probably function as sexual attractants.
Blarina brevicauda, and presumably
B. carolinensis and B. hylophaga
(the short-tailed shrews), have a toxic
venom in their saliva that may help
them subdue small prey.
Some shrews are mostly nocturnal;
others are active throughout the day
and night. They frequently use the tunnels
made by voles and moles. During
periods of occasional abundance,
shrews may have a strong, although
temporary, negative impact on mouse
or insect populations. Many predators
kill shrews, but few actually eat them.
Owls in particular consume large
numbers of shrews.
Some shrews exhibit territorial behavior.
Depending on the species and the
habitat, shrews range in density from 2
to 70 individuals per acre (1 to 30/
hectare) in North America.
Legal Status
Shrews are not protected by federal
laws, with one exception. The southeastern
shrew (Sorex longirostris fischeri)
is protected in the Great Dismal
Swamp in Virginia and North Carolina
by the Endangered Species Act of
1973. Nowak and Paradiso (1983:131)
list the following additional species or
populations of concern: Sorex preblei,
Sorex trigonirostri, and Sorex merriami in
Oregon; Sorex trigonirostri eionis in
Florida along the Homossassee River;
and Sorex palustris punctulatus in the
southern Appalachians.
Some states may have special regulations
regarding the collection or killing
of nongame mammals. Consult your
local wildlife agency or Cooperative
Extension office for up-to-date
information.
Damage Prevention and
Control Methods
Exclusion
Rodent-proofing will also exclude
shrews from entering structures. Place
hardware cloth of 1/4-inch (0.6-cm)
mesh over potential entrances to
exclude shrews. The pygmy shrew
(Sorex hoyi) may require a smaller
mesh. Coarse steel wool placed in
small openings can also exclude
shrews.
Cultural Methods
Regular mowing around structures
should decrease preferred habitat and
food, and may increase predation.
Where shrews are eating tree seeds,
plant seedlings instead to eliminate
damage.
Repellents
No repellents are registered for use
against shrews.
Toxicants
No toxicants are registered to poison
shrews.
Fumigants
No fumigants are registered for use
against shrews. It would be impractical
to use fumigants because of the
porous nature of typical shrew
burrows.
Trapping
Mouse traps (snap traps), box traps,
and pit traps have been used to collect
shrews. Set mouse traps in runways or
along walls, with the traps set at a
right angle to the runway and the triggers
placed over the runway (Fig. 2a).
Small box traps can be set parallel to
and inside of runways, or parallel to
walls around structures (Fig. 2b). Bait
the traps with a mixture of peanut butter
and rolled oats. A small amount of
bacon grease or hamburger may increase
the attractiveness of the bait.
A pit trap consists of a gallon jar or a
large can sunk into the ground under a
runway until the lip of the container is
level with the runway itself (Fig. 2c).
Bait is not necessary. A small amount
of bacon grease smeared around the
top of the container may be an effective
attractant, but this may also attract
large scavengers. Pit traps are more
effective for capturing shrews than
snap traps, although the increased labor
involved in setting a pit trap may
not be justified when trying to capture
only one or two animals. Monitor pit
traps daily, preferably in the morning
before the temperature gets hot,
although Churchfield (1990) recommends
checking traps four times in a
24-hour period. Place cotton wool in
the pit trap containers to reduce the
mortality of trapped animals. This is
especially important to ensure the successful
release of nontarget animals.
Since shrews are generally beneficial in
consuming insects, live-captured animals
can be relocated in suitable habitat
more than 200 yards (193 m) from
the capture site.
The traps and placement procedures
described above are also effective for
catching mice. Note the identification
characteristics given above for determining
whether the captured animal is
indeed a shrew. Sometimes birds are
captured in traps set for shrews. If this
Shooting
Shooting is not practical and is not recommended.
It is illegal in some states
and localities.
Other Methods
Owls may reduce local populations of
shrews in poor habitats, but this has
not been documented. Domestic cats
appear to be very good predators of
shrews, although they seldom eat
them (presumably because of the
shrew’s unpleasant odor). Cats may be
effective at temporarily reducing localized
shrew populations living in poor
cover around structures. Cat owners
may find dead, uneaten shrews
brought inside the home. Rather than
reduce the shrew population outside
to prevent this, simply monitor locations
regularly used by your cat, and
dispose of dead shrews by placing a
plastic bag over your hand, picking up
the dead animal, turning the bag
inside out while holding the shrew,
sealing the bag, and discarding it with
the garbage. Using a plastic bag in this
manner reduces the potential for flea,
tick, helminth parasite, or disease
transmission.
Economics of Damage
and Control
No studies concerning the economics
of shrew damage and control are available.
In Finland, shrews appear to play
a more important role as predators of
conifer seeds than they do in North
America. Overall, the economics of
damage by shrews is not considered
great.
*The above information was taken from a University of Nebraska Web site with
express permission of Stephen Vatassel, wildlife damage project coordinator.
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