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University
of Rhode Island GreenShare Factsheets
Spiders
Myths and a few fatal poisonings have made many people
afraid of spiders. The only dangerous spiders in the northeast,
however, are the very rare black widow and brown recluse spiders.
These spiders are not native to the northeast, but may be occasionally
transported here (the brown recluse is from the southwestern
United States and the black widow is from the southern United
States). Other spiders may be annoying due to their webs, but,
unpopular as they are, most spiders are shy and harmless to
humans. Most have fangs too small or weak to puncture human
skin. They usually will not attempt to bite unless accidentally
trapped or held. Spiders are beneficial, feeding on harmful
insects (flies, crickets, etc.) and mites in and around the
home, yard, garden and field
Spiders have eight legs (four pairs), and lack wings
and antannae, but all vary in size, shape and color. They have
two body regions: a cephalothorax (fused head with thorax)
and an abdomen. Most spiders have eight eyes, some only six
and several have fewer or none. All have a pair of jaw-like
structures (chelicerae) which are hollow claw-like fangs through
which venom can be ejected. The tip of the abdomen has silk-spinning
glands. Young spiders (spiderlings) resemble adults except
for their smaller size and coloration. Males are usually smaller
than females.
All spiders produce venom that is poisonous to their normal
prey of insects, mites and other small arthropods. Venom is
injected through the fangs to immobilize the prey. Since spiders
can only ingest liquids, digestive fluids are either injected
or regurgitated into the prey.
Spiders produce silk, secreted as a liquid through the
spinnerets, which hardens on contact with air. Different types
and textures of silk may be used to construct snares or webs,
egg sacs, draglines and ballooning threads. Some spiders use
web snares to trap prey, and all species construct a silk sac
to deposit eggs. Many spiders attach draglines of silk to the
substrate at intervals wherever they go, appearing to have
a silk thread to hang onto when knocked from their perch. Some
spiderlings sail through the air (ballooning) on wind currents.
Young spiders climb to a high point and release silk strands
until the drag from the wind is sufficient to support their
weight. They then release their hold and sail away, often for
considerable distances. These ballooning threads (gossamer)
can fill the air on clear days as spiderlings disperse to new
areas.
Spiders lay eggs within a silken egg sac that is often
ball-shaped and either hidden in the web or carried by the
female. Spiders may produce several egg sacs, each containing
several hundred eggs. One female may produce as many as 3,000
eggs in a series of several sacs over a period of time. Eggs
may hatch a few weeks later (or the following spring). Spiders
reach adulthood in one year. For a spider to grow, it must
shed its skin (molt) usually four to twelve times before maturity.
Most spiders live either one to two seasons. Spiders may overwinter
as eggs, spiderlings in the egg sac, immature spiders living
outside the egg sac or as adults.
Orb Weaver or Garden Spider (family Araneidae): These
spiders all construct the characteristic circular, flat wheel-like
web (orb web) in which flying insects are trapped. Some construct
elaborate and beautiful, large webs in gardens and tall vegetation,
especially obvious in the late summer and early autumn months.
They have poor vision and locate the prey by feeling the vibration
and tension of the threads in their web and then quickly, by
turning the captive with their legs, use silk to wrap the victim.
The prey is bitten before being carried to the center of the
web or to a corner where it is eaten. Anything inedible is
cut out of the web and dropped to the ground. In the fall,
female orb-weavers die soon after producing egg sacs containing
several hundred eggs. Eggs may hatch soon after or not until
the following spring. Many adult spiders are large, some with
oddly shaped abdomens (pointed spurs, conical tubercles, etc.,
in various colors of black, yellow, orange, red, white, brown,
green, etc.).
One common garden spider, known as the black and yellow
garden spider, has silver hairs on the back of its forward
body section and a large abdomen marked in black and bright
yellow (or orange). The common garden spider is approximately
25 mm (1 inch) long and hangs head down in the center of the
web. It is often found in brambles, bushes and tall grasses
in open, sunny places near human habitations where flying insects
blunder into the trap. Egg sacs are spherical and narrowed
at one end and covered with a tough brown, paper-like silk.
These spiders are not considered dangerous, despite their formidable
appearance, but they can bite if handled or molested.
Wolf Spiders (family Lycosidae): Female wolf spiders
are large, hairy, running spiders, often confused with tarantulas.
They may be brown, black, gray, white, yellow, orange or green.
Many have a stripe or pattern the length of the first, and
sometimes the second, body segment. They are nocturnal and
usually occur outdoors but may wander indoors, especially into
cellars and basements in late summer and fall when cooler temperatures
prevail. These hunting spiders, which do not construct webs,
carry the large, globular egg sac attached to spinnerets under
the abdomen. Upon hatching, the spiderlings climb onto their
mother's back and ride there for several days before dispersing.
They do not establish themselves indoors and are not aggressive,
but may bite if handled or molested.
Jumping Spiders (family Salticidae): These common
spiders are no more than 12 mm (1/2 inch) long, and are striking
in appearance, with bright colors often heightened by iridescent
scales. They are hairy and short-legged and can jump several
times their own length. Some are black with spots of orange
or red on the top surface of the abdomen; others are brownish-gray
and yellow with whitish markings. Their movements are quick
(irregular gait) with short, sudden jumps. Jumping spiders
are active during the day and like sunshine, normally living
outdoors, but are sometimes found indoors on walls, windows,
screens, doors, etc. They are sometimes carried indoors on
firewood. They depend on their vision (keenest of all spiders)
and leaping ability to catch prey, especially flies. After
mating, the female constructs a silk cocoon for her eggs and
guards it. Some can bite humans if handled.
House or Cobweb Spider (family Therididae): The
female house spider is larger than the male, about 10 mm (1/3
inch) long, gray to brown with a rounded, globular abdomen
mottled with several dark stripes on the upper side. House
spiders spin their webs in dark corners of moist rooms and
outdoors. They hang upside down in the center of an irregular
cobweb. Sticky threads on the outside of the web entangle many
insects, especially flies, which are bitten and sucked dry.
Females are fertilized several times during a lifetime and
lay up to nine egg sacs, each containing 200 or more eggs.
Young hatch in about eight days, staying within the sac until
after the first molt. Spiderlings take several months to mature.
Cellar Spiders (family Pholcidae): Cellar spiders
have bodies which are about 2-6 mm (1/16-1/4 inch) in length
and long, slender legs. Although similar in appearance to daddy-long-legs,
cellar spiders have rounded or elongate bodies which are light-colored,
gray or brown. Common in barns, cellars and damp warehouses,
they hang upside-down under sheetlike or irregular webs.
Brown Recluse Spider (Loxosceles reclusa): Brown
recluse spiders belong to a group of spiders commonly known
as violin spiders or fiddlebacks, because of a characteristic
fiddle-shaped pattern on their head region. The brown recluse
is golden brown with a dark brown or black "fiddle," which
is often shiny. They range from 5-15 mm (1/4 to 3/4 inch) long.
Brown recluse spiders are found primarily in the South and
Midwest. They are rarely, if ever, found in Rhode Island. Brown
recluse spiders live in basements and garages of houses, often
hiding behind boards and boxes. Bites sometimes occur when
the spiders hide in towels or clothing. They are seldom aggressive
and bite only when threatened or injured.
The severity of the bite of the brown recluse may vary
from no symptoms at all to a reaction that is very severe.
Often there is a systemic reaction within 24-36 hours of the
bite characterized by restlessness, fever, chills, nausea,
weakness and joint pain. There is often tissue death at the
site of the bite. In some severe cases, a wound may develop
that lasts several months. In all cases, a physician should
be notified. If at all possible, kill and take the spider to
the physician for positive identification. It is important
to note that many wolf spiders are similar in appearance to
the brown recluse, but the wolf spider is hairy, larger and
more robust than the brown recluse.
Black Widow Spider (Latrodectus
mactans): Like
the brown recluse, black widow spiders are not generally found
in Rhode Island, except when brought here by travelers. The
female is usually black with a red spot or hourglass-shaped
mark on its round abdomen. The male usually has light streaks
on its abdomen. The spider is about 38 mm (1 1/2 inches) in
diameter, including legs. In infested areas, black widow spiders
are common around wood piles, and are frequently encountered
when homeowners carry firewood into the house. They are found
under eaves, in boxes, outdoor toilets, meter boxes and other
undisturbed places. The female black widow occasionally eats
the male after mating (hence the name). She hangs belly-upward
and rarely leaves the web. The black widow is not aggressive,
but it will bite instinctively when touched or pressed. Be
very careful when working around areas where black widow spiders
may be established. Wear gloves and pay attention to where
you are working. Black widow bites are sharp and painful, and
the victim should seek medical attention immediately.
Sanitation is critical in successful spider control. Indoors,
the spiders, webs and egg sacs can be collected and destroyed
with a strong suction vacuum cleaner. Move and dust often behind
and under furniture, stored materials, wall hangings and corners
of ceilings. Eliminate other household pests (prey) such as
flies, ants and pantry pests, which attract spiders. Be sure
to control excess moisture and humidity, keeping basements,
crawl spaces, porches, etc., as dry as possible. Outdoors,
clean up woodpiles, trash, rocks, compost piles, old boards
and other debris around the house foundation where spiders
often live. Be sure to seal or caulk cracks and crevices around
windows and doors and install tight-fitting screens as needed
where spiders can enter the house. Use a hose with high-pressure
water on the outside of the house to knock down and destroy
webs, egg sacs and spiders. Use yellow or sodium vapor light
bulbs at outside entrances to reduce night-flying insects (prey)
which attract spiders.
We generally do not recommend insecticides for spider
control, but when necessary, spiders can be killed with aerosol
cans of either flying insect killer or residual sprays such
as crack and crevice sprays.
Adapted from the
Virginia Cooperative Extension and the Ohio State University
Extension, 1999
Pesticides
are poisonous! Read and follow all safety precautions on labels.
Handle carefully and store in original containers out of reach
of children, pets or livestock. Dispose of empty containers
immediately, in a safe manner and place. Pesticides should never
be stored with foods or in areas where people eat.
When trade names are used for identification, no product endorsement
is implied, nor is discrimination intended against similar materials.
Be sure that the pesticide you intend to use is registered for
the state of use.
The user of this information assumes all risk for personal injury
or property damage.
For more
information, call the URI CE Gardening and Food Safety Hotline
at 1-800-448-1011 or (401)874-2929 from outside Rhode Island;
Monday-Thursday between 9 am and 2 pm.
University
of Rhode Island Cooperative Extension provides equal program
opportunities.
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