How to Identify Dangerous Spiders by Their Abdomens
It is easy to identify most venomous spiders that live in the United States by looking at their abdomens. The abdomen is the back section of the spider that is the farthest from the animal's head. The spider's legs are not attached to its abdomen.
To tell if a spider is a venomous brown recluse, first look at its eyes--it should have six. Examine its abdomen. If the abdomen is thin rather than rounded and if the spider's head has a violin-shaped marking, it is a venomous brown recluse. The part of the marking that looks like the neck of the violin points towards the spider's abdomen.
Check under the abdomen of a shiny black spider. If there is a bright reddish orange marking that looks like an hourglass, it is a female black widow spider.
Stay away from a spider with red legs, a red head, and a shiny black abdomen which has bright red spots surrounded with yellow on top. This is a red widow spider, related to the black widow species, whose venom is also very toxic. Another related spider, the brown widow, is more difficult to spot. Its round abdomen is brown or tan that is marked with a contrasting colorful spot on the bottom side. Both of these spiders are native to Florida.
Look for yellow markings on the abdomen of a brown spider to see if it is a venomous hobo spider. These spiders live in the northwestern areas of the continental United States.
Observe the texture of the abdomen and other body parts of a black spider to see if it looks like soft brushed black cotton fabric. This is what a venomous black house spider looks like. If, however, the black abdomen of the spider belongs to a spider with a red head and a set of fat fangs, it is probably a dangerous mouse spider.
Get medical attention immediately if you are bitten by any of these spiders or if another kind of spider bites you and you have an allergic reaction.
Lesley Barker, director of the Bolduc House Museum, authored the books "St. Louis Gateway Rail—The 1970s," published by Arcadia, and the "Eye Can Too! Read" series of vision-related e-books. Her articles have appeared in print and online since the 1980s. Barker holds a Bachelor of Arts in sociology from Washington University and a Master of Arts in Teaching from Webster University.