Spiders

KEY PHYSICAL CHARACTERISTICS

All spiders have eight legs and two body regions - a cephalothorax (fused head and thorax) and an abdomen In contrast, insects have six legs and three body regions. Spiders also lack wings and antennae. All spiders have a pair of jaw-like structures known as chelicerae. Spinnerets, the silk-spinning glands used for making webs, are located at the tip of the abdomen.

LIFE CYCLE

Spiders reproduce by laying eggs contained in an egg sac. These sacs are usually ball-shaped and are generally carried by the female or hidden in webs. Most sacs contain about 100 or more eggs which hatch in about three weeks. After several molts, adulthood is reached in approximately one year.

HABITS

Because spiders feed entirely on living insects or other animals, they may actively search for their prey, hide and wait for them to pass, or build webs to trap flying insects. Most web-spinning spiders build and abandon several webs per year. The webs are produced by glands on the spider's abdomen. The silk is a liquid which hardens when exposed to the air. Silk is used to construct webs, safety lines, and egg sacs, and is used as parachutes for traveling long distances.

Perhaps two of the most feared and misunderstood spiders are the black widow and the brown recluse. Both have venom, both are poisonous and both can bite people.

Almost all spiders found in California are harmless to humans and most species do not attempt to bite unless they are provoked. Spiders usually remain hidden and do not seek out and bite humans. Most spiders cannot penetrate the skin of a human with their fangs.

• The Black Widow is most easily identified by the red hourglass shape on the underside.
• The Brown Recluse is most easily distinguished by the violin-shaped mark located behind the eyes. There are 3 pair of eyes on this species while most spiders have 4 pair.

Bites caused by Black Widows or the Brown Recluse are rare. If you are bitten try to capture the spider for identification and seek medical attention.

OTHER SPIDERS

Orb-Weavers

There are several hundred species of orb weavers in the United States. Usually only the large, conspicuous orange and yellow or black and yellow species are noticed in late summer when they build webs that extend 1 foot or so across on porches or small trees and shrubs. These large flat webs have many straight strands radiating out from the center and are connected with spiral thread winding around and around from the middle out to the perimeter. The spiders, often with bodies 1 inch long and very long legs, sit in the center of the web waiting for flying insects to be trapped.

Cobweb Spiders

Cobweb-weaving spiders make small, irregular webs. These webs are characteristically found indoors in the upper inside corners of window frames. There are many species of cobweb spiders and the black widow is one of them. Most of them are smaller than the black widow. They have the same type of globular abdomen, but it is always dull in color and not as eye catching. These quiet spiders hang in the web and wait for small insects to wander into their snares.

Wolf Spiders

The hairy wolf spiders are very common outdoors under leaf litter, rocks, and logs. When they come inside, they normally stay on the ground floor and are active in dim light. Large wolf spiders often frighten people. If handled, they give a painful bite, but it is not dangerous.

Jumping Spiders