How to Determine If a Spider Is Poisonous in North America

Although there are several North American spiders that have poisonous bites, only six are dangerous to humans. Of these, only two are considered deadl-- the brown recluse and the black widow spider. Learning to identify poisonous spiders can help you avoid a trip to a emergency room.

Difficulty: Moderately Easy

Instructions

1. Check the back. Is the spider brown with a dark violin-shaped mark on its cephalothorax (the body segment the legs attach to)? If so, then it is a deadly brown recluse spider.

2. Check the abdomen. Does the spider have distinctive yellow or red marks on the underside of the abdomen? If so, then it is probably a deadly black, brown or red widow spider. The marks may or may not resemble an hourglass--consider any mark an indication that the spider is a widow. Some widow spiders also have marks on the back of the abdomen. Is the spider brown with chevron-shaped marks on the abdomen and you live in the northwest part of North America? If so, then it is a poisonous hobo spider. Male hobo spiders have mouth parts that look like boxing gloves.

3. Check for burrows. Is it a large, fat, black spider with fangs? Then it is a poisonous mouse spider. Male mouse spiders have red heads. Both live in deep ground burrows. Is it a mottled gray and brown spider found in or near a silk-lined burrow on the ground? It may be a poisonous wolf spider.

4. Check the body. Is it a small black spider with a velvety covering on its body? It may be a poisonous black house spider, especially if it was found in or near a messy web.

5. Check the color. Is the spider yellow? It may be a poisonous species of yellow sac spider.

Tips & Warnings

• Although spiders eat other insects, they most often eat those that are beneficial rather than pests.
• Many spiders may bite, especially if threatened. It's possible that a spider bite may cause a severe allergic reaction in some people even if the spider isn't normally considered dangerous. Pets, small children and the elderly are particularly at risk from spider bites. Therefore, seek medical attention for any painful spider bite or if you become ill after spending time in spider habitats, such as woodpiles, sheds and basements.

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[cgarrett006]

on 9/28/2008 Good points, Conal.

Another misleading point is the tip that, "Although spiders eat other insects, they most often eat those that are beneficial rather than pests." This is entirely untrue. Beneficial how, exactly? The beneficiality of an insect species is an immeasurable attribute and is dependant intirely upon the point of veiw of the persn making the assessment. Spiders serve as a check-and-balance system to the insect world. Spiders are effectively the population control of most all insects and help to keep the ecosystem balanced.

[Conal]

on 8/19/2008 For more accurate information on this topic, visit http://www.chirurgeonguild.org/documents/articles/all-stings-considered.pdf

[Conal]

on 8/19/2008 I must say this is an extremely biased and misleading article. Please note the excessive use of the adjectives "Deadly" and "Poisonous."
Sorry to say, spiders hardly deserve the label "Deadly." Despite Hollywood’s claims, people simply don't die in minutes after being bitten, nor is there any spider whose bite kills even 1% of the people it bites. Even the Australian Funnel spider, oft named the most deadly spider on earth can't meet that claim. In fact, there have been no deaths from a Funnel spider bite in almost thirty years!
As far as "Poisonous," that is even more ludicrous. There are no spiders on the planet that are poisonous. You can eat as many of them as you like. They may not taste good, but they won’t kill you.
Spiders are venomous. Not poisonous.
On to a little more detail.
Claiming a spider with a violin-like mark on its cephalothorax is a very poor way to