Pest Control – Spiders

Spiders are arachnids, a group of arthropods that also includes scorpions, harvestmen, mites, and ticks. Approximately 3,500 species occur in North America.

Spiders have jointed legs and a hard exoskeleton. Spiders have four pair of legs, with a body divided into two regions (cephalothorax and abdomen), while insects have three pair of legs and the body divided into three regions: head, thorax, and abdomen. Spiders have no wings or antennae, but have enlarged, sharply pointed jaws called fangs (chelicerae).

All spiders are predators and feed on living prey. Spiders attack and subdue their prey by biting with their fangs to inject a poison. In general, spiders are considered beneficial due to their ability to reduce insect populations.

All spiders spin silk, but the silk is used in a wide variety of ways. Most spiders construct a silken case to protect their eggs, but not all spiders make a web. A few use silk threads much like a parachute to aid in dispersal on wind currents.

All spiders are poisonous, but fear of all spiders is unwarranted because most are either too small or possess poison that is too weak to harm humans. A few spiders have bites that are dangerous to humans, and the bite of these few species can cause serious medical problems and possible death under certain circumstances.

The most dangerous spiders to humans in The Northwest are the Hobo Spider and the black widow. If you have a spider problem in your home or business, schedule an estimate today.

Problem Spiders

Widow Spiders (Family Theridiidae).

spiders_11Five species of widow spiders occur in North America. However, the single species found in Washington is the western black widow Latrodoctus hesperus. This spider is not found west of the Cascades. The adult female is a velvety jet black, but males and immatures are striped with white or yellow. The underside of the abdomen of the adult female usually shows reddish markings that resemble an hourglass. The back of the abdomen is usually entirely black, but may be marked with a broken stripe of white, red, or yellow spots.

An adult female, including legs, is about 1 1/2 inches in diameter. This species is usually associated with dry, undisturbed piles of firewood, old lumber, dry crawl spaces, outbuildings, rock piles, or bales of hay. Widow webs are poorly defined, amorphous sheetings of very strong, fine silk.

The bite of the adult female is more toxic than that of juveniles or males. However, widows are shy, retiring spiders and bite only reluctantly, usually only when molested.

Widows are more aggressive when they are protecting an egg sac. The bite of the widow spider causes little immediate pain and may go unnoticed. Slight local swelling and reddening at the bite site are early signs, followed by intense muscular pain, rigidity of the abdomen and legs, difficulty in breathing, and nausea. There is little first aid advised other than cleaning the bite and calming the victim. Consult a physician as soon as possible. Pain can be relieved with injections of calcium gluconate. In untreated cases symptoms generally fade in 2 to 3 days. Widow bites are more dangerous if the victim is a small child or an elderly person.

Brown Spiders (Family Loxoscelide).

spiders_4The Brown Recluse is included here due to numerous misidentifications of spider bites in Western Washington.

The brown recluse spider is common in the southern states, but is sometimes transported into other areas in cargo or in motor vehicles. However, the brown recluse does not normally occur in the Pacific Northwest. The only specimen of the brown recluse ever collected in the Pacific Northwest was found in Prosser in 1978. This spider came from a trailer of household goods brought into the area from Kansas. No additional specimens have been collected.

These spiders also are known as fiddlebacked or violin spiders, as they have a dark violin pattern on the front portion of the body. They have only three pair of eyes instead of four like most spiders. Their overall size is 3/4 to 1-1/4 inches in diameter. Brown recluse spiders vary in color from tan to dark brown. They readily enter human dwellings and hide during the daytime in cracks, behind or in furniture, or in undisturbed piles of clothing.

The bite of the brown recluse spider either may go unnoticed with no aftereffects or may be followed by a severe localized reaction characterized by scabbing, sloughing off of affected tissue (tissue necrosis), and very slow healing. Again, as with other suspected spider bites, consult a physician if pain and other discomfort follow the bite.

Hobo Spider (Family Agelenidae).

spiders_2The Hobo Spider, Tegenaria agrestis, is a member of the family Agelenidae, commonly called funnel-web spiders or funnel weavers. These spiders build funnel shaped webs in dark, moist areas, often in basements, and sit in the mouth of the funnel waiting for prey. The funnel opens at both ends, and the web expands outward into a broad, slightly curved sheet. Hobo spiders are of European origin. They were probably introduced to this country very early through commerce.

The Hobo Spider is one of the most common spiders found in houses in the Pacific Northwest. Although this spider was first reported in Seattle in 1930, it did not become common in the Pacific Northwest until the 1960s. In the Pullman, Washington – Moscow, Idaho area, it is prevalent in basements and in window wells of houses. It is usually found only on the ground or lower floors. This spider was previously named the “aggressive house spider” because it bites with little provocation when cornered or threatened.


The Hobo Spider is a relatively large, swift running spider. Mature adults range from 1 to 1 3/4 inches including legs. As with most spiders, males can be identified readily by the expanded, swollen tips of their palps. Sexually mature males and females are abundant from mid-summer (July) through fall. During this period males tend to wander relatively long distances in search of females. Eggs are laid into a spherical silken sac spun by the female, usually in September or October. The sac is then placed within or adjacent to the funnel, usually on the underside of a rock or other object. This sac is usually covered with a thin layer of soil, wood chips, or other debris, including prey. The debris coated sac then is often covered with another layer of silk. Eggs hatch the following spring. Most Hob Spiders molt about 10 times over a span of 2 years before reaching sexual maturity. Immatures are commonly found wandering in the spring searching for web sites.

Investigations of Hobo Spider bites show the venom produces skin injuries, or lesions, similar to those produced by the Brown Recluse. Therefore, ulcerating lesions of this type occurring on humans in Washington, Oregon, and Idaho are almost exclusively due to bites by the Hobo Spider. Surprisingly, males are somewhat more venomous than females. Bites commonly occur as a spider is squeezed against the body when a homeowner picks up a firewood log with a spider on it or when a spider is located in an article of clothing and is squeezed when the clothing is put on. The initial bite is not painful. It has been described as producing a very slight prickling sensation. However, a small, insensitive, hard area appears within 30 minutes or less, and is surrounded by an expanding reddened area. Within 15 to 35 hours the area blisters. About 24 hours later the blisters usually break, and the wound oozes serum. A cratered ulcer then develops a crust to form a scab. Tissues beneath the scab may die and slough away. In some cases the loss of tissue may become so severe that surgical repair is needed. The fully developed lesion can vary from about 1/2 to 1 inch or more in diameter. Lesions may take several months to heal, and frequently leave a permanent scar.

Systemic illness may or may not accompany the bite. However, the most common symptom is a severe headache, sometimes occurring within 30 minutes, usually within 10 hours, that does not respond to aspirin. The headache may persist for 2 to 7 days, and is sometimes accompanied by nausea, weakness, tiredness, temporary loss of memory, and vision impairment. The symptoms are similar to those experienced with migraine headaches. Bites by Hobo Spiders have produced few unconfirmed deaths; however a person bitten by one of these spiders should seek immediate medical treatment.


Other common spiders of Western Washington

spiders_5Jumping Spiders (Family Salticidae).

These compact, active, and usually colorful spiders often are found on window sills and ceilings where they stalk and pounce on unsuspecting flies and gnats. They are considered harmless.




Orb Weaving Spiders (Family Araneidae).

spiders_6These belong to the largest family of spiders. All construct the circular, flat, wheel-like web in which they trap flying insects. The very large black and yellow garden spider is a typical example.





Hackled Band Weavers (Family Amaurobiidae)

spiders_7A robust spider, Callobius severus 3/4″ diam, is a common crawl-space inhabitant of houses in western Washington. These large, impressive spiders are harmless to humans and pets.




Cellar spiders (Family Pholcidae)

spiders_8These spiders are common in cellars, crawlspaces and garages. Their webs are irregular tangles. This spider is considered harmless to humans.



Daddy Long Legs (Order Opiliones)

spiders_10Daddy-longlegs are not really spiders at all they are in their own separate Order which is Opiliones. Daddy Long Legs spiders are gray to light brown in color. They are characterized by having one basic body segment which shows segmentation on the posterior portion, at most 2 eyes and all 8 legs attach to the pill-like body segment, four pairs of long, slender legs that may be up to 30 times as long as its body, causing them to appear much larger than they actually are. A common wives tale is that they are the most poisonous spider, but have mouthparts too weak to penetrate human skin. This is false; they actually have no venom at all.

Preventive Control

spiders_3Repair holes large enough to admit spiders. Other areas to inspect include entry points of water pipes and electrical lines. Caulk any cracks and other small openings. Before bringing firewood into your home, inspect it for spiders or their egg sacs. In addition, keep woodpiles and other debris away from the house. Use a good vacuum that will readily remove all spiders and webs from corners and nooks. Crush spiders by stepping on them as they run across floors, or capture them with your vacuum; they will die rapidly in the dry, enclosed bag. Depending on the type of vacuum used, it might be best to dispose of the vacuum bag immediately after capture so the spider will not escape.

If spiders are numerous and constantly entering the house, you may want to Call Action Pest Control Inc. to eliminate the unwanted intruders.