Quick Facts...
- Spiders feed solely on insects and other arthropods. This makes them
beneficial in helping manage pests.
- Some spiders wander indoors in the early fall when cooler outdoor
temperatures force them to find shelter.
- Some spectacular spiders are found in webs outdoors in late summer,
particularly the banded argiope and the “cat-face” spiders.
- Common spiders found indoors include funnelweb spiders, cobweb spiders,
cellar spiders, and sac spiders.
Spiders are beneficial arthropods, that survive by feeding on insects.
Oftentimes they are the most important biological control of insect pests
in gardens, fields, forests, and homes. However, their presence is a cause
of concern to some people. Many people fear spiders beause of stories
or myths. Others object to spiders because of their habit of building
webs in and around the home. There are a few spiders whose bite require
medical attention, but these are very rare in Colorado.
Spiders differ from insects in that they have eight legs (rather than
six) and only two body regions (instead of three). The body regions include
the cephalothorax (head and legs) and the abdomen. On the head are usually
six to eight eyes, often arranged in pairs. The pattern of eye arrangement
is characteristic for the different spider families.
Some spiders capture prey by using webs and venom. Others are active
hunters that ambush or capture prey. These spiders physically overpower
their prey and then use venom to immobilize them.
Life Cycle
Females lay eggs in clusters of up to several dozen. Most cover the eggs
with a sheet of tough silk that can attach to almost any surface. The
eggsac of many web-spinning species are found in and around the webs which
the females usually guard. Females of some species (wolf spiders, cellar
spiders, nurseryweb spiders) may carry the eggsac until the eggs hatch.
Young spiders, known as spiderlings, emerge from the eggsac and disperse.
Many climb to the top of a nearby object, produce long filaments of silk
(known as gossamer), and become carried by the wind. This method of dispersal
is known as ballooning. Spiderlings can be carried long distances using
this method. Because spiders have a great ability to disperse, in addition
to other factors that affect their survival, the number of spiders found
in an area from one season to another naturally varies. Also, spiders
are able to rapidly recolonize areas even if they have temporarily been
eliminated.
Most spiders in Colorado have a life cycle that spans one year. However,
widows and some wolf spiders can live up to a few years, and tarantulas
can survive a decade or more.
Adult male spiders are smaller than females, sometimes dramatically smaller.
Males are identified by the presence of an enlarged pair of palps (mouthparts)
which may appear somewhat like miniature boxing gloves or a fifth pair
of legs. The palps are used to transfer sperm. Male spiders are often
more commonly found in homes as they tend to wander during the mating
season in search of females.
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Figure 1. Funnel web spider.
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Figure 2: Funnel web spider.
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Common Colorado Spiders
Funnel web spiders (Agelenidae)
Funnel web spiders, or grass spiders, are the most common spiders found
in homes, particularly during late summer and early fall. They produce
dense mats of silk in areas such as shrubs, thick grass, or corners of
buildings. A central retreat (the base of the “funnel’) is usually
used by the spider which then moves rapidly onto the web when prey enter
onto it.
Funnel web spiders are harmless but are often mistaken for the brown
recluse, a potentially poisonous species that does not naturally occur
in Colorado. Funnel web spiders differ from the brown recluse in that
they have a darker brown color with black markings on the abdomen, lack
the characteristic “violin” marking on the cephalothorax, have
four pairs of eyes instead of three, have striped legs, and are considerably
faster.
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Figure 3. Jumping spider (Phidippus).
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Figure 4. Jumping spider.
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Figure 5. Jumping spider.
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Jumping spiders (Salticidae)
Jumping spiders are active hunters. They stalk and pounce on their prey
rather than use silk to snare it. They are capable of jumping short (.5
inch) distances, possess large eyes, and the most common species are brightly
colored. As with almost all spiders, jumping spiders use silk to lay down
a trail, cover its eggs, and construct temporary shelters.
Ground spiders (Gnaphosidae)
Ground spiders, as their common name implies, are most often found under
rocks or logs where they build silken retreats and emerge only to hunt.
Some species wander indoors when the weather turns cold. Ground spiders
are harmless to humans.
Cobweb spiders/House spiders (Theridiidae)
Cobweb spiders are common inhabitants of dark corners around the home.
They have a generally bulbous body and create messy webs with sticky threads.
The majority of these spiders are harmless, although one group, the widow
spiders in the genus Latrodectus, are potentially dangerous. The family
also includes spiders in the genus Steatoda that are also generally black
and sometimes mistaken for widow spiders, but they have a large white
band and lack the orange-red hourglass pattern.
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Figure 6: Cellar Spider
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Cellar spiders (Pholcidae)
Cellar spiders are usually found in dark corners of cellars, crawl spaces,
and garages. They are very long-legged and often confused with daddy-long-legs.
However, they are true spiders that spin untidy webs which are often quite
extensive. When disturbed, they characteristically bounce in the web.
Female cellar spiders carry eggs by her jaws in a loose silk sac until
they hatch.
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Figure 7: Dysdera crocata.
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Dysdera crocata (Wood Louse Hunter)
This hairless spider is perhaps best marked by its large fangs which
it uses to feed on pillbugs (roly-polies) and other hard-bodied prey.
When full grown they are about .5 inch in length. Dysdera have a generally
creamy gray body with distinctly reddish legs and cephalothorax. They
live in a silk retreat and hunt at night. Their bite can be painful but
they are not aggressive. Their venom is not known to cause medical problems.
Sac spiders
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Figure 8. Yellow Sac Spider.
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Sac spiders are active hunters. They get their name because they spend
daylight hours in a flattened silken sac, typically located in the upper
corners of rooms or in wall cracks. Most sac spiders are pale colored.
They are usually the most common spider found wandering in homes during
fall, particularly at night. Cheiracanthium species are suspected
as being the most common source of spider bites in homes.
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Figure 9. Female wolf spider with spiderlings on her back..
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Figure 10. Burrowing wolf spider.
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Wolf spiders (Lycosidae)
Wolf spiders are active hunters that do not produce a snaring web. They
may make a silk lined retreat in soil, under rocks or in other protected
sites. Most are grey or brown and some are quite large including the giant
wolf spider (Hogna carolinensis) and some burrowing wolf spiders
(Geolycosa spp.) which are commonly mistaken for tarantulas. Smaller
species somewhat resemble funnelweb spiders.
An unusual habit of wolf spiders is that the females carry the egg sac
on their hind end. The newly hatched young continue to live on her back
for the first few weeks of life.
Wolf spiders occasionally enter homes, particularly in areas of new development
where their habitat was disturbed. They are normally shy and not dangerous
to humans, although large species can bite.
Araneus spiders (Araneidae)
Several orb weaving spiders of the genus Araneus are commonly found outdoors
late in the season. They are usually brownish in color with a large and
prominent abdomen that is dimpled and marked. Some species, known as “barn”
or “garden” spiders, make geometric webs among vegetation, buildings,
windows, or outdoor lighting.
The largest and most commonly observed species is the “catface”
or “monkeyface” spider, Araneus gemmoides. Large females may
be more than .25 inch in diameter and are generally round with a prominent
pair of humps on the back. Araneus spiders are harmless.
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Figure 11. Tarantula.
| Tarantulas (Theraphosidae)
Tarantulas are found in southeastern and southwestern Colorado. Mature
male spiders are commonly observed when they wander across roads in late
summer in search of females. Tarantulas are among the longest lived of
all spiders. Females may live for more than 20 years. Populations of tarantulas
tend to be localized, where they burrow into soil and feed at night. They
rarely enter homes and are essentially harmless. They may produce a pinching
bite if handled. Tarantulas defend themselves by flinging hairs from their
abdomen which can be irritating to the touch.
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Figure 12. Banded garden spider.
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Banded Garden spider (Araneidae)
The largest and most striking of the orb weaving spiders found in Colorado
is the banded garden spider (Argiope trifasciata). It is found in late
summer and early fall among shrubbery and in gardens where they make a
highly symmetrical orb web. Females are generally silvery, with dark and
yellow striping. Males are rarely observed and are much smaller than the
females. The banded garden spider is harmless.
Potentially Dangerous Spiders
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Figure 13. Female black widow with egg sacs.
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Figure 14. Female black widow.
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Figure 15. Male black widow spider.
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Widow Spiders
Widow spiders, particularly the western widow (Latrodectus hesperus)
are common in Colorado. They usually nest near the ground at dark, undisturbed
sites. Window wells, entrances to crawl spaces, old rodent burrows, corners
of garages, and abandoned rodent burrows are some of their favorite nesting
sites.
The presence of red or red-orange markings on the underside of the abdomen
are characteristic of widow spiders. This pattern may be in the form of
a distinct hourglass pattern or appear as two separate triangles. The
markings may be distinct and bright, or sometimes faint and indistinct.
Overall color of the adult females is uniform black, although immature
stages and males may have brown, red, and white markings on the back.
Some non-poisonous spiders that are commonly mistaken for widow spiders
are Steatoda species (cobweb spiders), mentioned earlier.
Bites from the widow spider are painful and potentially dangerous because
they contain a nerve poison. Fortunately, widow spiders are non-aggressive
and rarely bite. When bites do occur they happen when the female is provoked,
for example, when an unwitting person presses down on a spider that is
resting beneath a log or rock.See fact sheet 5.605,
Western Widow Spider for additional information.
Brown Recluse spider
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Figure 16. Brown recluse spider (male) showing distinctive pattern on back.
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Figure 17. Brown recluse spider.
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The brown recluse (Loxoceles reclusa) is rare in Colorado because
of our cold winters and dry climate. However, it is common to areas along
the southern Mississippi Valley and are occasionally brought into the
state. Brown recluse lives within a loose, messy web in dark corners of
buildings.
Brown recluse spiders are pale brown or buckskin colored with long, dark
brown legs. A violin shaped dark marking is present behind the head, and
the abdomen is uniformly colored. Unlike most spiders, the brown reclude
possesses only three pairs of eyes. They are commonly mistaken for funnelweb
spiders, certain wolf spiders, and even sun spiders.
The venom of the brown recluse is damaging to human cells. In susceptible
individuals a slow-healing, ulcerous wound may form at the bite site.
Oftentimes the original bite is not noted, but after a few hours a blister
will form and pain develops. For more information see fact sheet 5.607,
Brown Recluse Spiders in Colorado: Recognition and Spiders of Similar
Appearance.
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Figure 18. Hobo spider.
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Figure 19. Hobo spider, distinctive markings on the underside of abdomen.
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Hobo spider
A European species of funnelweb spider, known as the ‘hobo spider’
(Tegenaria agrestis), is slowly spreading across western North
America and was recently found in Colorado. Some reports indicate that
bites of this spider may also produce wounds similar to that of brown
recluse. Hobo spiders are closely related to other Tegenaria species,
known as European house spiders, that are not poisonous.
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Figure 20. Hairy desert scorpion.
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Figure 21. Daddy-long-legs.
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Figure 22. Solpugid or sun spider.
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Spider Relatives
Scorpions
Scorpions are arachnids that have an elongated abdomen tipped by a stinger.
A portion of their mouthparts (pedipalps) are modified as pincers. Scorpions
found in Colorado capture and kill their prey primarily using these large
pincers. Only when necessary do they bend the stinger over their body
and inject poison into the prey. Species found in Colorado are not dangerous
to humans although the sting can be painful.
Daddy-long-legs (Harvestmen, Phalangids)
Daddy-long-legs are not true spiders, but are arachnids placed in another
order (Opiliones). You commonly encounter them outdoors, particularly
when adults are present in late summer and early fall. Because they are
active around harvest time, one of their common names is ‘harvestmen’.
Daddy-long-legs are characterized by extremely long legs and a body that
is not distinctly separated into regions. Unlike spiders, daddy-long-legs
do not possess poison glands nor do they produce silk. A common, worldwide
‘urban legend’ about daddy-long-legs is that they are “the
most poisonous spider, except their fangs are too small to pierce human
skin.” This is completely without foundation.
Sun Spiders/Wind Scorpions/Solpugids
Sun spiders are bizarre looking arachnids (Order: Solifugae) most common
to southeastern Colorado. Occasionally they are found along the Front
Range. They possess large conspicuous jaws used to crush prey, but they
do not have venom glands. Also present are prominent enlargements of the
mouthparts (palps) that give the impression of a fifth pair of legs. Sun
spiders are active animals, and a common name ‘wind scorpion’
reflects this behavior. They occasionally enter buildings, particularly
in early summer. Sun spiders are discussed in more detail in fact sheet
5.589, Sunspiders (Windscorpions).
Spider Bites
Most spiders are not aggressive and bite only when trapped against the
skin. If a bite is suspected or is known to have occurred, follow these
first aid steps recommended by the American Red Cross:
- Treat the site of the bite with an antiseptic to prevent infection.
- Apply ice to the site of the bite to reduce pain and swelling.
- If a black widow or brown recluse spider is suspected, or if serious
symptoms develop such as increasing pain or swelling, consult a physician.
If at all possible, bring the spider to the physician’s office.
Effective antivenins are available for black widows, but they can only
be used if the spider that inflicted the bite is positively identified.
It should be stressed that spider bites are difficult to diagnose correctly
as there are many other medical conditions that mimic the same symptoms.
Spider bites, particularly those of “brown recluse spiders,”
are greatly overdiagnosed in Colorado.
Controlling Spiders Around the Home
From a biological standpoint, it is rarely necessary to control spiders.
However, if it is desirable to get rid of spiders in the home, a combination
of sanitation and pesticides should be effective. Pesticides alone, without
some effort to remove or modify favorable spider habitats, will not be
effective.
Remove rocks, wood piles, compost piles, old boards, and other sheltering
sites adjacent to the home. Eliminate migration of spiders into homes
by caulking cracks and crevices around the foundation. Make sure all screens
and doors are sealed tight. Keep crawl spaces free of debris and limit
boxes and other potential hiding places from basements and other dark
storage areas. Regularly vacuum or brush spider webs. The elimination
of other insects that are prey can limit spider development.
Occasional spiders can be removed by hand (wear gloves or grasp the spider
with a tissue) or with a vacuum. Sticky traps, used to control cockroaches
and rodents, can capture spiders when placed along baseboards or other
migration areas.
Residual insecticides can be used to control spiders when applied to
corners and other sites where spiders tend to breed. Household insecticide
products containing various pyrethroids (bifenthrin, cyfluthrin, permethrin,
tetramethrin) are commonly available for this purpose and should be applied
in accordance with the label’s instructions. Total release foggers,
containing pyrethrins, probably will have little effect on spiders.
Where spiders and webbing occur in nuisance numbers on the outside of
buildings they can be washed off with a forceful jet of water. Reduction
of outdoor lighting, or replacing lighting with yellow or sodium vapor
lights that are not attractive to insects, can limit spider web building.
Dark colored siding seems to be less attractive than white siding to the
insects on which spiders feed.
Further Reading:
- Foelix, R. 1993. Biology of Spiders. Harvard University Press, Cambridge,
MA.
- Gertsch, W.J. 1979. American Spiders. Van Nostrand Reinhold Co., New York.
- Kaston, B.J. 1978. How to Know the Spiders. Wm. C. Brown Co., Dubuque,
IA.
- Levi, H.W. 1996. A Guide to Spiders and Their Kin. Golden Press, New York.
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