Welcome To The World Of Spiders


There are over 35,000 species of spiders worldwide, with about 3,000 occurring in North America. Many species of spiders are household pests. Wherever their food is available, spiders are likely to be found. All spiders are predators, feeding mainly on insects and other small arthropods. In the United States only two spider groups are considered dangerous to man, the black widow spiders and brown recluse spiders. Both of these groups are composed of several species.


Non-insect arthropods with 2 body regions, cephalothorax (head and thorax) and abdomen connected by a tiny waist (pedicel). Antennae absent. Usually 8 simple eyes, occasionally 6. Below eyes are 2 chelicerae or jaws which end in a hollow fang, connected internally to a poison duct. With 1 pedipalp (palp) between chelicerae and lst pair of legs on each side. Legs slender, 4 pairs. Abdomen unsegmented, with a group of fingerlike spinnerets (produce silk) on posterior or rear end. Males usually smaller than females and with terminal pedipulp segment greatly swollen, may also differ in coloration. The immature stages are egg and spiderlings, the lafter closely resemble the adults except for size and sometimes coloration.


Since the black widow and brown recluse spider groups are of primary importance in human environments, their identification is essential. For both groups, several species are involved which can only be separated by experts. However, group recognition alone is sufficient for PCO purposes. Consult the individual treatments which follow this introductory section for details. For general recognition of many common spiders, you can try to match your specimen to the pictures presented in "Spiders and Their Kin" by Levi et.al. which is in the Golden Nature Guide series.


Female spiders usually do not eat their mate after copulation. In a week or more after mating, the female deposits as few as 20-30 to several hundred eggs in a silken sac. Depending on the species, one or more sacs may be made. Species which tend their egg sacs or young usually produce fewer eggs. It may be weeks later, or not until the following spring, before the spiderlings hatch and/or emerge from the 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 and provides for general dispersal of the species. Spiderlings go through 4 to 12 molts before maturity. Most spiders live for 1 or 2 seasons, but a few live from 5-20 years. Spiders are predators, paralyzing or killing their prey with venom. They typically feed by injecting a predigestive 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 or active at night and will scurry away when disturbed unless they are tending egg sacs or young. During the day, they usually remain hidden and inactive in cracks and crevices, their webs, etc. Spider bites usually result only with great provocation such as squeezing or handling. Bites usually occur when the males are wandering about searching for females or when people clean out neglected places such as basements, attics, or garages, or put on seldom-used clothing. Many spiders cannot penetrate human skin with their fangs and the bite of those that can, usually results in no more than a slight swelling and inflammation. The primary exceptions are the black widow and brown recluse spiders. The black widow spiders possess a neurotoxin whereas, brown recluse spiders possess a cytotoxin which may produce an ulcerating sore or lesion; antitoxins are available for both. Always consult a physician if a spider bite is suspected. It is particularly important to capture and take the suspect spider along for identification purposes.