These animals are not insects, but arthropods. They have two body regions, cephalothorax and abdomen connected by a tiny waits. They have no antennae, 4 sets of legs and 8 simple eyes, sometime 6. Below they eyes are two jaws which end in a hollow fang that are connected internally to a posion duct. The males are usually smaller than females and may differ in coloration.
The immature stages are egg and spiderlings, the latter closely resemble the adults except for size and coloration in most cases.
Many spiders are associated with moisture and, therefore, are found in basements, crawl spaces, and other damp parts of buildings. Others will live in warm, dry places so are found in subfloor air-vents, in upper corners of rooms or in attics. All spiders in the Northwest prey on insects or whatever they can capture.
There are about 3,000 species in North America and 35,000 in the world. Females usually do not eat their mates after copulation (except for the Black Widow). In a week or more after mating, the female will lay anywhere from 20-100+ eggs in a silken sac. Depending on the species, one or more sacs can be spun. Species that tend to their eggs or young usually produce fewer eggs. It can take weeks or until the following spring before the spiderlings hatch from their sac.
The early instars and sometimes the males of many species will climb to a high point within suitable air currents, spin silk threads into the air and float out on the breeze like kites (this is called ballooning).
Spiderlings go through 4-12 molts before maturity. Most spiders live for 1 to 2 years.
All spiders are predators, paralyzing or killing their prey with venom. They feed by injecting a pre-digestive fluid into the body of their prey and then suck in the digested liquid food. Spiders can survive without food for several weeks to a few months.
Most spiders are nocturnal and will scurry away when disturbed unless they are tending egg sacs or young. During the day, they usually remain hidden. Spider bites usually result only with great provocation such as squeezing or handling. Many spiders cannot penetrate human skin with their fangs. Always consult a physician if a spider bite is suspected and also try to bring the suspected spider along for identification purposes.