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Spiders

Scientific name: Araneae

Common species: (in Northern California) Grass Spider, Cellar-Spider (also known as Daddy Long Legs Spiders), Gray Wall-Jumper, Mouse Spider,  Black Widow, Orbweavers, Garden Spiders

Average size: Spider sizes vary greatly depending on species and can range from <0.1-4.0< inches

Commonly found: On walls and floors, in corners and hard-to-reach places.

Diet: Insects

General characteristics and facts:

  • There are over 38,000 known species.
  • They have 8 legs and no antennae.
  • Spiders are not insects, they are in the Arachnid family.
  • A cobweb is an abandoned spider web.
  • All spiders use venom to kill their prey, however only a very small percentage of species have venom strong enough to harm a human.

Below are some of the more common species that pose problems in our area.

Wolf Spiders

Biology: Wolf spiders are hunters, and use their silk only for lining a nest and for covering their eggs. The females create the tough egg sac and then carry it attached to the tip of the abdomen. Once the eggs hatch the mother then cuts a slit in the sac to allow her young to emerge, and they then climb onto her abdomen to be carried around for up to 2 weeks. Some species of wolf spiders may have leg spans of 4 inches or more and they are very mobile, very fast, and very aggressive when threatened. They are capable of biting humans but the venom is not considered dangerous, but their aggressive behavior makes wolf spiders some of the most feared by people. Smaller species may even “run” across the water of a swimming pool, suspended on the surface tension of the water. Retreats for the spiders are holes in the soil, under debris on the ground or within wood piles. They commonly enter structures and can be found running across floors or walls as they search for food.

Identification: Wolf spiders vary in size from small species with only ½ inch leg spans to large ones whose legs may stretch out 5 inches. In general they are long legged and covered with short hairs, gray to brown to dark brown in color, and with several darker stripes running longitudinally on the cephalothorax. These body region is somewhat pear-shaped, with the front much narrower than the back and with the front, when viewed from the side, sitting higher than the back. However, the eyes are distinctive, with 8 ocelli arranged in the following manner. The “face” area is usually perpendicular, and the hind pair of ocelli sit at the top of the face, a very large pair of ocelli sit facing directly forward, and 4 smaller ocelli are in an arc below this enlarged pair.

Characteristics Important in Control:  General cleanup of unnecessary debris outside will reduce harborage sites, and cleanup of clutter in garages or storage areas will reduce the numbers of spiders living on the interior. If invading spiders become a problem they can be prevented with an application of a residual pyrethroid insecticide around the building exterior and in likely pathways along walls on the inside.

Funnel Web & Hobo Spiders

Spiders

Funnel Spider

Common Name: Funnel Web or Hobo spider
Latin Name: Tegenaria agrestis
Common Family Name: Funnel web spiders
Latin Family Name: Agelenidae

Other Names: Aggressive house spider, funnel weavers, domestic house spider

Origin: At least 7 species of funnel web spiders in North America. The family contains many other genera and over 400 species of spiders.

Biology: The most notorious species in this group is called the Aggressive House Spider or Hobo Spider, and it is known to bite with little provocation. Like many spiders it has venom which is cytotoxic, and tissue death at the site of the bite, leading to a lingering open wound, is very possible. It is a very common spider in structures in the Pacific Northwest, and is the most likely cause of serious spider bites there. They usually live about two years, and with the first year spent developing to the adult stage, the second summer is for mating and egg production, and the adults die shortly after this. The “funnel” name is derived from the web shape of these spiders, which create wide mat of webbing with a funnel-like hole in it.  After building the web, the spider waits within this funnel for prey to stumble onto the web mat. The spider then rushes out, subdues the prey, and drags it back into the funnel for feeding. The funnel-web mats may be on vegetation or near the soil, or possibly within structures in undisturbed areas.

Identification: These are fairly large spiders, with adult bodies about ¾ inch long and with very long, hairy legs. There are several longitudinal dark stripes on the top of the head and the thorax, also the top of the abdomen exhibits a distinct “herring-bone” pattern of darker, zig-zag lines. There are eight eyes, arranged in two rows across the front of the head, and with the posterior row strongly curved to the back, and the outer pairs of eyes nearly touch.

Characteristics Important in Control: Since these spiders pose a definite human health threat, they should be controlled when found living in structures. Removing all possible harborage sites, is the first line of defense. Exterior vegetation should be trimmed well away from any structures. Also grassy areas should be kept mowed, and piles of lumber or firewood maintained well away from the building. Any unnecessary debris or items sitting on the soil should be removed.  Cleanup of any clutter the interior of buildings and structures is important to reduce places of hiding and harborage, along with physical removal of webbing. Also, any potential gaps or holes the spiders may use to enter the building should be plugged. Chemical applications include the use of a dust insecticide within cracks and voids that may harbor the spiders, as well as an application of a residual insecticide.

Black Widow Spider

Black Widow

Common Name: Spider – Black widow
Latin Name: Latrodectus
Common Family Name: Comb-footed spiders
Latin Family Name: Theridiidae

Other Names: Brown widow

Origin: Five species of these native spiders occur in North America, being found in all states. Other species may be found worldwide.

Biology:  Black widow spiders are the most dangerous spiders with respect to human health in the U.S. They are one of the few spiders capable of biting humans, injecting them with a neurotoxin which can be injurious and potentially fatal. Only female black widows bite humans, but both males and females construct webs to capture other prey, primarily flying insects. Males also enter a female’s web for mating, and if the female is not receptive, the male very well may be eaten, hence the reason for the name of this spider. The life span of black widow females averages around 180 days as an adult, taking about 3 months to reach maturity. Males mature in about 70 days and live only about 30 days after that. The female may produce up to 9 egg sacs with about 350 eggs per sac on average. She will be most aggressive and defensive of her webbing while she is guarding these eggs, and will also have a voracious appetite during this period. The new spiderlings emerge from the sac and remain near it for a day or two, but then they undergo “ballooning” to disperse, creating long silk strands that are carried away by the wind. Black widows are generally reclusive spiders that create their webs in areas of warmth and inactivity. The web is made of extremely strong silk that is very sticky, and often makes crackling sounds when moved.  It also has a very haphazard appearance without the symmetry usually seen in other spider’s webs.

Identification: Females are the most recognized spider in North America, with their shiny black body, long thin legs, large oval abdomen, and red “hourglass” pattern on the underside of the abdomen. However, this hourglass pattern may not always be there. Males also have the same pattern, but it is white, and their body color is mottled brown and white. New born spiders begin very light colored and progress to the adult color in stages as they pass through their development, gradually becoming more black if they are females. The female tends to hang upside down in her web due to the weight of the abdomen. Eggs sacs of black widows are about ½ inch in diameter and are smooth surfaced. The eyes of comb-footed spiders are typically arranged in two rows of four eyes, one row above the other and with the eyes so close together that they touch each other.

Characteristics Important in Control: Elimination of unnecessary debris in storage or on the exterior of structures will reduce harborage sites, including lumber or firewood piles, boards or other materials on the ground, and yard debris.  The individual spider inside may be eliminated by vacuuming, and then sweeping the web away with a broom.

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