|Spiders have an ominous, but often undeserved
reputation. Though most spiders are venomous and considered predators, of the
thousands of species found in Canada, few are actually considered a health
threat. In fact, spiders are actually helpful in controlling other pests in the
home or garden since they feed on other insects and spiders. They generally
bite and inject venom into their prey. Spiders, however, rarely bite humans.
Although spiders are often unpopular, the venom
of most species is not very toxic to humans, usually resulting in no more than a
slight swelling, inflammation, or itching sensation. Most spiders’ fangs are too
small or weak to puncture human skin. Spiders usually will not attempt to bite
unless accidentally trapped against the skin or grasped, although some species
actively guard their egg sacs or young.
Two spiders that can be a health risk are the
brown recluse and
One of the most common misconceptions about
spiders is that they are insects. Spiders are arachnids and are actually
closely related to mites, ticks and scorpions. Spiders have two body parts (cephalothorax
and abdomen), eight legs and usually six to eight eyes, while insects are
classified by having three body parts (head, thorax and abdomen), six legs, and
generally two compound eyes or up to three single eyes. The average life span
of a spider is usually one to two years, but some can live five years and up to
Life Cycle and Habits
Spiders lay eggs within a silken egg sac that is
often ball-shaped and either hidden in a web, affixed to a surface, or carried
by the female. Spiders may produce several egg sacs, each containing up to
several hundred eggs. A spider grows by shedding its skin (molting), usually
four to twelve times before maturity. In many species, the mature male often
wanders about in search of a mate. Some species of spiders may live for years,
but most spiders only survive for one season.
All spiders produce silk, which is secreted as a
liquid through the spinnerets and hardens on air contact. Spiders use silk for a
variety of purposes, such as making egg sacs, capturing prey, holding prey,
making shelters or retreats, and transferring sperm during mating. Also,
spiderlings extrude silk threads that enable them to be transported by air
currents, a process called “ballooning.”
Spiders are predators that typically feed on
living prey. They produce venom that is poisonous to their normal prey of
insects, mites, and other small arthropods. Venom is injected through the hollow
fangs to immobilize the prey and begin the digestion process. Spiders can only
ingest liquids, so they either inject or regurgitate digestive fluids into the
prey. They then suck in the digested liquid food.
Spiders use a variety of tactics to capture
prey. Some species are web builders that use webbing to ensnare their prey.
Others are active hunters that actively search for their prey. Passive hunters
are spiders that lay in wait for their prey rather than searching for it.
simplest method of controlling spider infestation is to reduce the pest
population (other insects) inside the home so they seek a more dependable food
supply outside the home. Control of spiders is best achieved by following an integrated pest
management (IPM) approach that involves multiple tactics, such as preventive
measures, exclusion, sanitation, and chemicals applied to targeted sites. IPM
requires a thorough inspection of the building to locate the pest and its
harborages. An inspection should be done at night if the species is nocturnal.
An important first step is to correctly identify the spider, as this
determines which management tactics to adopt that take into account specific
biology and habits. For example, if the spider is a web builder, control efforts
should target its web because that is where this spider spends most of its time.
On the other hand, active hunters are spiders that move about widely, and some
species are most likely to contact insecticide-treated surfaces at ground level.
Within each of the following categories, particular tactics may be more or
less applicable, depending on the species of spider:
- Shake out clothing and shoes before getting dressed.
- Inspect bedding and towels before use.
- Wear gloves when handling firewood, lumber, and rocks (be sure to inspect
the gloves for spiders before putting them on).
- Remove bedskirts. Move the bed away from the wall.
- Don’t store boxes and other items underneath beds.
- Exercise care when handling cardboard boxes (some spiders may inhabit the
space under folded cardboard flaps).
- Install tight-fitting screens on windows and doors; also install weather
stripping and door sweeps.
- Seal or caulk cracks and crevices where spiders can enter the house.
- Equip vents in soffits, foundations, and roof gables with tight-fitting
- Install yellow or sodium vapor light bulbs outdoors since these attract
fewer insects for spiders to feed upon.
- Many web-making spiders set up residence near lights that remain on at
night. Locate such lights away from the house or turn them off when not
- Tape the edges of cardboard boxes to prevent spider entry.
- Use plastic bags (sealed) to store loose items in the garage, basement,
- Remove trash, old boxes, old clothing, wood piles, rock piles, and other
- Eliminate clutter in closets, basements, attics, garages, and
- Store items off the floor and away from walls in basements, crawl spaces,
attics, garages, and outbuildings in order to reduce spider harborage sites.
- Eliminate household pests (prey) such as flies, ants, and cockroaches that
- Do not stack wood against the house.
- Remove heavy vegetation and leaf litter around the foundation.
- Wash spider webs off the outside of the house using a high-pressure hose.
- Capture the spider and release it outdoors. An effective technique for
capturing hunting spiders is to place a cup over the spider and then slide a
piece of paper underneath to entrap it.
- Dust and vacuum thoroughly to remove spiders, webs, and egg sacs (dispose
of the vacuum bag in a container outdoors).
- Outdoors, use a water hose or broom to regularly destroy any webs that are
constructed on or around the house. Spiders often move elsewhere when their
webs are regularly destroyed.
- Use a rolled up newspaper or fly swatter to kill individual spiders.
- Use sticky traps or glueboards to entangle spiders.
- Eliminate or shield outdoor lights or bright indoor lights that attract
the spiders’ insect food source.
- Trim vegetation around the building foundation and remove debris to
discourage insects and spiders from living next to a structure.
- Seal openings and install screens and door sweeps to prevent spiders (as
well as other unwanted pests) from moving indoors.
There are many labeled pesticides for spider control. Some are labeled for
homeowner use, while others are labeled only for the licensed, certified
pesticide applicator. If insecticides are used, read the label and follow the
directions carefully. A pest professional is familiar with the safe use of
insecticides and may be the best choice to safely control spiders. (Directory
of Canadian pest professionals)
Individual exposed spiders can be killed with a nonresidual aerosol spray,
but any egg sacs will be unaffected. It generally is best to use a vacuum
cleaner so that the egg sac is removed from the premises.
For web builders, insecticide treatments should be applied so that the
chemical contacts spiders in their webs. A nonrepellent insecticidal dust is
useful to treat webs because the dust clings to the silk and is likely to be
contacted by the spider. Residual dusts can be applied to voids and inaccessible
areas where spiders may hide.
A wettable powder or microencapsulated “slow-release” formulation of a
residual insecticide can be applied to corners, behind and under furniture,
behind stored items, etc. to control active hunting spiders. This approach also
is useful to prevent establishment of new spiders. Aerosol flushing agents such
as pyrethrins, though ineffective by themselves in providing long-term control,
can cause spiders to move about so that they contact treated surfaces.
Residual liquid sprays can be applied to the outside perimeter of the home
(including under eaves, patios, and decks; behind window shutters), cracks and
crevices of decorative molding, undisturbed corners, and other suspected spider
harborages. Residual liquid sprays applied to the outside perimeter of the home
are not very effective for species that display web-sitting behavior.
Link to Black Widow and Brown Recluse
slideshow that includes identification,
habits, symptoms of their bites and effect of their bites.
Spider Identification photos and descriptions
list of the spiders of BC,
The two most common spiders that are
considered health threats are
the black widow and brown recluse.
The brown recluse spider (Loxosceles spp.) is a poisonous spider that is
light brown in color. It is about 1/2 inch in length, has a violin-shaped
marking on the thorax (mid-section) and is sometimes called a fiddleback
spider due to the unique markings. While most spiders have 8 eyes, the
brown recluse has 6 (3 pairs). The brown recluse spider received its
name because of its color and reclusive behavior. These spiders make an
irregular and sticky web that is used for shelter rather than for trapping
There are seven species of brown recluse spider that are a health concern in
the United States. Though active throughout the year, they often go
unnoticed because of their reclusive habits. Adults may be found in dark,
secluded indoor places that are dry, cluttered, undisturbed and contain a
supply of insects for food. They are most commonly found behind baseboards,
under tables and chairs, in the basement, crawlspace, attic, infesting cedar
shake roofs, and in garages and sheds. Another common hiding place for a
brown recluse is in garments that are left hanging undisturbed for some time
and in the linens of beds that have been unoccupied for a long while. Bites
often occur when the spider is trapped in shoes or clothing, rolled on while
in bed, and encountered when cleaning storage areas.
The brown recluses venom is a cytotoxin that
attacks the cells of flesh and produces necrosis or dead tissue in humans.
Though fatalities from the venom are very rare, the reaction to the venom
depends on the amount of and individual sensitivity to the toxin. The bite
is not usually felt, but a stinging sensation may develop shortly after,
followed by intense pain. The reaction, however, may not occur until an
hour or more after the bite. The bitten area will first develop a small,
white blister and enlarge to the size of a silver dollar as the venom
attacks and kills the tissue in the affected area. Eventually, the affected
tissue will die and leave a sunken, ulcerated sore. The healing process is
slow, generally six to eight weeks. If bitten, call a physician or go to
the emergency room immediately. If possible, exterminate the spider and
take it along for identification purposes. Though no antitoxin is available,
prompt medical treatment can prevent severe reaction and minimize the extent
of damaged tissue and eventual scarring.
To avoid getting bitten by the brown recluse, shake out unworn or stored
shoes and clothes before wearing, check bed linens of unoccupied beds and
wear leather gloves when working around potential habitats. Use caution
around spider webs in basements and crawlspaces. If a brown recluse is
encountered, contact a pest control professional.
The female black widow spider (Latrodectus spp.) is a poisonous spider
that has a somewhat round, shiny black abdomen with red markings that
resemble an hourglass on the underside. The size of the body is
approximately 1/2 inch wide and 1 1/2 to 1 3/8 inches long. Despite common
opinion, the female rarely kills the male after mating.
Five different species of the black widow spider are prevalent in North
America. They generally live under rocks and under fallen trees outside the
home. In and around the house they are often found in firewood piles,
They are also found in secluded places, such as garages and sheds. They
feed on insects and other spiders that are trapped in their web. They are
usually not aggressive spiders, but if handled or accidentally touched, they
The black widow’s venom is a neurotoxin that attacks the nervous system
and may cause pain and serious illness in humans. Though the bite is not
often felt, pain will develop immediately. Reactions to the black widow’s
venom include increased body temperature and blood pressure, profuse
sweating, dizziness, blurred vision, nausea, and pain and swelling around
the bite. Antitoxin is available to combat the neurotoxin. If bitten, call
a physician or go to an emergency room immediately. If possible,
exterminate the spider and take it along for identification purposes. Bites
are rarely fatal when promptly treated, however, small children are at
To avoid getting bitten by the black widow, wear leather gloves when
working around potential habitats. Use caution around spider webs in
basements and crawl spaces. If a black widow is encountered, contact a pest
The university of Arkansas has a good web page on Black Widow Souders
is brown in color and its body is
about 3/8-inch long. Its abdomen is spherically shaped, and is white to
brown in color with several dark markings. Males are smaller than females,
and their legs are orange in color. The female's legs are yellow. This
spider is the most common type of comb-footed spider, a group that includes
the black widow species. They are urban
pests named after the comb-like row of bristles located on the tarsi of
their fourth pair of legs. House spiders
are common throughout the world, and their webs are most often found in
corners, basements, crawlspaces, under
furniture and around windows. The venom
is necrotic, causing open, localized
wounds that may be slow to heal
but Despite its aggressive nature, reported
bites from this spider are relatively rare.
|Source: New Age encyclopedias, Truman's scientific guide to pest control
operations ( Purdue University), Compton's ency. on CD, Random internet
British Columbia Ministry of Forests,
7380 Puckle Road, Saanichton BC V8M 1W4
“ . . . spiders are ruthless storm troops in the matriarchal anarchy
that is the arthropod world: theirs is the most diverse,
female-dominated, entirely predatory order on the face of the earth. As
such, spiders are key components of all ecosystems in which they live.”
there are approximately 700 spider species known from British Columbia.
A complete introduction to spiders will appear here shortly. In the
here to read Robb Bennett's paper on the spiders of British Columbia
(PDF). (Bennett, R. G. 2001. Spiders (Araneae) and araneology [the study
of spiders] in British Columbia.
Journal of the Entomological Society of
British Columbia, 98:85-92. Posted with permission of the ESBC.)
paper on Canadian spider diversity and systematics (PDF). (Bennett,
R. G. 1999. Canadian spider diversity and systematics.
Newsletter of the Biological Survey of
Canada [Terrestrial Arthropods) 18(1):16-27. Posted with
permission of the BSC(TA)].
Some notes about spiders that are of real or
imaginary medical interest:
recluse spider (Loxosceles reclusa): There
are no brown recluse spiders in BC or in Canada. Their range is limited
to the south-central and mid-western US.
Click here for a general account about the brown recluse spider,
where it occurs, and how to identify it. For a more detailed account of
the biology of brown recluse and related spiders in North America
(including medical information), read this
article published in The Journal of Arachnology by well-known brown
recluse spider specialist Rick Vetter.
Pasted from <http://www.geog.ubc.ca/biodiversity/efauna/spiders.html>
Links to Other spider pages
Spider Identification photos and descriptions
Spiders In and Around Homes
Spiders at Ojibway. Windsor, Ontario
An incredible variety of these fascinating arthropods inhabit every habitat
at Ojibway. By late summer spider numbers can grow to 100,000 per hectare,
supported by the immense insect population at that time of year.
Spiders of North-West Europe
Arachnology home page
Central European Spiders
Groupe d'etude des Arachnides, Lionel Dabat
Arachnids, arthropods, reptiles of Europe
Arachnoligische gesellschaft e.V.
Aracnis, European spiders & their kin
Belgian spider site from Gie Wyckmans
French jumping spiders from Yvan Montardi
British Arachnological Society
Australian spider and insect bites
The Australian spider page from Glenda Crew
Robert Raven's Soapbox
Brisbane Spiders by Peter Chew
Brown recluse, univ of California
Spider Envenomations, Brown Recluse
Brown Recluse Spider, Ohio state univ
Recluse spiders, Hobo spider web site
Black widow spiders, Desert USA
Black Widow Spider, Univ of Michigan
Latrodectus species (German)
Hobo spider web site
Camel spiders or Solifugids
Webs of life
Arachnophilia, The wonderful world of spiders
Webs of Life
Salticidae of the world by Jerzy Proszynski
How Spiders Work
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