Spiders are arachnids, and have eight legs with two body sections. They do not have wings or antennae. The method spiders use to kill their prey is to inject them with a toxic venom. There are certain types of spiders whose venom is considered "poisonous" to humans.
The most common spider in California that presents a danger to humans is the black widow. Its body is black and slender, with a red or orange hourglass shaped mark on its abdomen. Another type of spider to be wary of is the recluse, which is a violin-shaped mark with the neck of the violin facing away from its head. These are poisonous to humans, although they do not target humans specifically.
Different types of spiders prefer different environments, although all spiders prefer the dark. Some thrive in damp areas, such as crawl spaces and basements. Others prefer warmer, dryer areas such as attics and corners of rooms. There are spiders that live in burrows instead of webs, and still others who live in crevices. Male spiders court females, and then the female spider creates an egg sac from which spiderlings are born. A spider's ability to create the silk it uses to make a web is also used to create the egg sac.