A list of the most common spiders found in California, with information on where they are commonly found and what they look like.
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Spiders are considered to be air-breathing arthropods with eight legs, chelicerae and fangs that can and will inject venom if threatened or disturbed. Spiders have been identified as the largest order of arachnids, ranking seventh in total species diversity among all other groups of organisms. We most frequently encounter in our homes, yards and out structures are the Wolf spider, Cellar spider, Black widow, Yellow sac spider and even occasional, although extremely rare in California, the Brown recluse.
The Wolf spider
The name Lycosidae, comes from the Ancient Greece meaning “wolf” as the Lycosidae or Wolf spider has very good eyesight and is an outstanding agile hunter.
The Wolf spider preys on insects that are crawling or resting on the ground. Wolf spiders actively hunt in the open during the day and night, often observed on the ground in litter and on low vegetation. The Wolf spider burrow is often found under debris or on soil. Instead of spinning webs to catch prey, make a small, thick web where they rest. Wolf spiders a distinctive pattern of eyes: four small eyes in front in a straight row, one middle pair of larger eyes, and one rear pair of widely spaced eyes on top of the head.
Adult Wolf spiders have been mistaken for young to juvenile Tarantulas as they have long hairy legs. They are usually black and white or strongly contrasting light and dark, which can make them difficult to discern unless they are moving. Currently, there is about 200 species in North America.
The Cellar spider
Cellar spiders have extremely long, skinny legs with small bodies that are usually tan or gray. The web of a cellar spider is usually very messy, similar to the web of a cobweb spider. Like all spiders, cellar spiders have 8 legs, 2 body parts, and fang-like mouthparts. The body length of adult cellar spiders about 1/4" or less.
The Black widow
The black widow spider, Latrodectus hesperus, is the most common harmful spider in California. Venom from its bite can cause reactions ranging from mild to painful and serious, but death is very unlikely and many symptoms can be alleviated if medical treatment is obtained. Anyone bitten by this spider should remain calm and promptly seek medical advice; it is helpful if the offending spider can be caught and saved for identification.
The typical adult female black widow has a shiny black body, slender black legs, and a red or orange mark in the shape of an hourglass on the underside of the large, round abdomen. The body, excluding legs, is 5/16 to 5/8 inch long. Only the larger immature female and adult female spiders are able to bite through a person’s skin and inject enough venom to cause a painful reaction.
The Yellow sac spider
The common, house-dwelling agrarian sac or yellow sac spider, Cheiracanthium inclusum, is a small spider that spins a silken sac web in the corners of ceilings and walls, and behind shelves and pictures; it is also commonly found outdoors in shrubbery. This spider is light yellow and has a slightly darker stripe on the upper middle of the abdomen. The eight eyes of this spider are all about equal in size and arranged in two horizontal rows.
Yellow sac spiders can be seen running on walls and ceilings at night and quickly drop to the floor to escape if they are disturbed. Bites usually occur when the spider becomes trapped against a person’s skin in clothing or bedding. It is estimated that sac spiders are responsible for more bites on people than any other spider. Typical symptoms of a bite include initial pain, redness, and sometimes swelling.
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