There are over 35,000 species of spiders in the world, about 3,000 are found in North America. Many spiders are pests you may find in your home. Spiders are predators, feeding on insects and small animals. In Canada, only one spider occasional may be of some danger to man, the black widow.
Because the black widow and brown recluse spider is important to humans it is important to identify them properly.
These spiders get their name from the popular belief that the female eats the male, this rarely happens.
Adult female body length is about 12-13 mm including an almost spherical abdomen about 7.2-9.6 mm in diameter, with overall length including legs of about 38-43 mm; males are about half the size of the female. Typically black, on the under side with a triangular reddish hourglass-shaped marking but sometimes separated ("splithourglass"); with red markings above spinnerets. Males usually with color pattern on top side, pattern may vary but usually consists of a row of red spots with white lines or bars radiating out to sides. With 8 simple eyes. The "western" Black widow and the northern widow both occur in Canada more likely in the West. Female black widow spiders deposit their eggs in silken egg sacs that are about 9.5-12 mm in diameter, white but soon turn pale brown. The female produces from 6 to 21 sacs and the average number of eggs per sac is about 450. The sac's outer covering is tough and closely woven. The incubation period ranges from 8 to 30 days.

When hatched, the spiderlings undergo the first molt within the sac. They go through 4 to 9 instars in up to 107 days, each instar having different coloration or color pattern.

Most spiders overwinter immature, develop into adults in the spring, and die in late July. They take about a year to grow from egg to adult. The number of survival days after maturity is from 822 to 952 for females and 127 to 196 for males. These spiders spin an irregular web and hang from it upside down. The web is used to ensnare prey. The female avoids light and tends to work at night.

Only the female bite is poisonous. Spiderlings are poisonous when ingested until they are 18 days old, and then loose their poison; adults have a different kind of venom.

The black widow's poison is a neurotoxin. The female is normally shy, but attacks immediately after egg laying and when guarding her eggs. The black widow bite is not always felt, so the only reliable evidence of a bite is a slight local swelling with 2 tiny red spots where the fangs entered. The pain is almost immediate and reaches its maximum in 1-3 hours, continues for 12-48 hours, and then subsides. The major symptoms are increased body temperature and blood pressure, profuse sweating, and nausea. There is an antitoxin available. Immediately call a physican or go to an emergency room if bitten. When treated, bites are rarely fatal except occasionally in small children. Initially, the second instant spiderlings remain near the sac but within a few days they climb to a high point within suitable air currents, spin silk threads and float out on the breeze. Outside, black widows live under stones and pieces of wood, in hollow stumps and trees, in rodent burrows, and occasionally in low tree branches or shrubbery. Favorite places are barns, outhouses, henhouses, sheds, garages, meter boxes and woodpiles. Indoors, they are found in seldom-used areas of garages, basements and in crawl spaces where their webs are usually about 30 cm in diameter. Female spiders do not eat their mate after mating. In a week or more, the female may deposit up to several hundred eggs in a silken sac. One or more sacs may be made. Spiders that tend their egg sacs or young usually produce fewer eggs. It may be 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. 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 some may live from 5-20 years.

Spiders are predators, paralyzing or killing their prey with venom. They 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 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 squeezing or handling. Bites often occur when people clean out places such as basements, attics, or garages. Many spiders cannot penetrate human skin with their fangs and the bite of those that can usually results in a slight swelling or inflammation. The exceptions are the black widow and brown recluse spiders. The black widow spiders uses a neurotoxin whereas, brown recluse spiders uses 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. Make sure that the building is in good physical condition, properly screened and sealed to reduce entry. Also, changing the bulbs near the entrances to yellow bulbs, may be of some help in reducing attractiveness. Consists of keeping the premises free of debris such as boxes, papers, clothing, scrap and lumber piles, etc.; it is wise to wear protective gloves and clothing when cleaning out such accumulations of clutter. A thorough housecleaning should be done twice each year. Remove spiders, webs, but especially the egg sacs with a vacuum, both inside and outside. Seal and dispose of the bag immediately. Chemical control consists of the application of appropriately labeled pesticides in spider harborages. If web-building spiders are the problem, lightly dusting the web with a non-repellent dust is very effective because these spiders recycle their silk.