GENERAL INFORMATION AND BIOLOGY
Few creatures are as feared and misunderstood as spiders. For the most part, spiders are harmless and generally beneficial by keeping the insect populations in check. Spiders are seldom aggressive and bite only when threatened or injured. Few spiders bite people and the venom of most is harmless. However, the bite of the hobo spider, black widow and the brown recluse (also known as the Recluse or Fiddle Back) can be quite dangerous. Beneficial or not, if spiders become a pest you need to go to our SPIDER ELIMINATION section, where you will find pesticide (such as Suspend SC) and non-chemical control methods. Most infestations require both methods. And remember, the better you understand any pest, the easier it will be to eliminate or control.
Spiders are the largest group of arachnids. There are more than 35,000 named species worldwide, including about 3,000 in North America, but probably most spider species are still awaiting identification. When someone brings a spider to us for identification, it is usually large (which makes one believe it might be a Tarantula) or is marked with brilliant colors (which many believe might be a black widow), but most spiders that we are asked to identify are harmless.
These predators live almost everywhere - on the ground, under rocks, inside and underneath playground equipment, among grasses, on plants, in tree branches, in underground caves and even on the water. Spiders frequently stray into dwellings or other indoor habitats, or may be accidentally introduced on firewood, laundry that has been hung out to dry, and on flowers. Spiders will also sneak into our homes in boxes, clothing or furniture. In windows and near outdoor lighting, web-building spiders often construct webs because insect prey may be attracted at night by the lights and by air currents.
Spiders are easily recognized by the 4 pairs of seven segmented legs and (like all arachnids) have a cephalothorax and abdomen. But unlike scorpions, mites and daddy-long-legs, the cephalothorax and abdomen of the spider are separated by a visible waist or pedicel. The top of the cephalothorax is protected by a shield-like covering called the carapace.
Most species have 8 simple eyes, although some have less and a few species have none. Often the number and arrangement of eyes are important in identifying the different families. Below the eyes are 2 small jaws (or chelicerae) that end in fangs. Venom is produced in glands and empties through a duct in the fangs. This venom is used to paralyze or kill prey. Then the spider crushes the victim by rubbing the chelicerae against each other and against the enlarged bases of the pedipalps, located before the first legs. There are usually 6 finger-like silk glands (spinnerets) located beneath the abdomen, just in front of the anus.
Not all spiders spin webs. Some live in burrows, which they line with silk, while others have no retreat at all. All young spiders and some adult males release long silken strands, which they use like a parachute to ride the wind to other areas. This process is called ballooning. For more information about webs and silk production, read spider web article.
Most spiders lay their eggs in silken egg sacs that are placed in the web, attached to leaves or twigs, or carried around by the spider until the eggs hatch. Spiderlings (as the young are sometimes called) resemble adults and are often cannibalistic. All spiders are predators and most feed on insects, although a few large species prey on small vertebrate animals.