Summarize this article:

Black widow spiders are found across the U.S and Canada, and in other temperate regions around the world. They are the most venomous spiders in North America. The female is the easiest to recognize -- and the most dangerous. She is coal-black, with a spherical abdomen and a red hourglass-shaped mark on her belly. Her body is approximately half an inch long, but she has a total length of 1.5 inches (3.8 cm) with her legs extended.  The male is about half the size of the female and is brown or grey. He usually has several red dots on his abdomen and may have a yellow or red band across his back. Male black widow spiders are not venomous. Young black widows, known as spiderlings, are white or yellow-white when they first hatch. They become darker as they grow. They may have yellow or red patches across their backs, resembling the adult male. It is impossible to tell male and female spiderlings apart. At this stage, both are harmless to humans. The black widow spider is timid and reclusive, preferring to make its home in dark, protected areas, such as in boxes, among firewood and under ledges. It is nocturnal, actively hunting at night.  The black widow spider's web is usually located within a foot of the ground. It is slightly erratic in appearance and made with stronger silk than most other spider webs. The web is used to catch prey and to hang the female's cocoon of eggs. Black widows are usually found in dark corners of the house or around the edges of a yard or garage where their webs will have a lesser chance of being disturbed. They may also be found under vehicles, even those that are being driven periodically. Check for webs near the tires, or under/around the engine. Black Widows are territorial, so their webs are often spaced about a foot apart. Female Black Widow spiders have very powerful venom -- in fact, it is said to be15 times stronger than that of a rattlesnake. The venom is a neurotoxin. Symptoms include muscle aches, abdominal pain, breathing difficulties and nausea. The majority of Black Widow bites are easily treated. However, if medical treatment cannot be administered on time, a Black Widow bite can lead to convulsions and death.  Black Widow spiders are not aggressive and will only bite as a defense mechanism. Most bites occur when the spider is accidentally disturbed or injured, and feels threatened. Small children, the elderly and the infirm are much more susceptible to adverse reactions when bitten by a Black Widow. Medical treatment should be sought immediately. . Another venomous spider which is slightly more common than the Black Widow is the Brown Recluse spider. These are harder to identify because they look like many other spider species, ranging in color from dark cream to brown. They are similar in size to the black widow and have a dark violin shaped mark on their back.  The venom of the Brown Recluse spider is not as strong as the Black Widow's, but their bite can lead to death. The methods for getting rid of Brown Recluse spiders are the same as for the Black Widow, so you can target both species at once.

Summary:
Recognize a black widow spider. Know its habits. Understand the dangers. Watch out for Brown Recluse spiders too