Venomous spiders in the United States vary from highly dangerous, like the brown recluse and the black widow, to the virtually harmless, such as the St. Andrews cross spider.

Often, spiders are referred to as "poisonous" but this is actually inaccurate. Spiders are venomous, not poisonous. The difference being that venom is injected through fangs or other devices into the bloodstream. Poison is ingested. In theory, for example, one could drink rattlesnake venom without much effect to their well being. Arsenic, a poison, would have a markedly different effect. DISCLAIMER - THIS IS NOT TO SAY THAT ONE SHOULD GO OUT AND DRINK VENOM IN ANY FORM. THAT IS DANGEROUS, IF NOT STUPID. It is just for the sake of distinction between the two types of toxicity.

That being said, spiders use venom to liquify their meals. They inject the venom, and it breaks down the insides of the prey to a drinkable "soup" that they then drink for food. This venom is also a means of defense when the spider is threatened.

As a rule, all spiders are venomous. The difference is that some spiders have venom that is dangerous to humans, and others have venom that is not. 

Now that you understand how venom works, let's look at a few spiders in the United States that you need to be aware of, as well as a few that ride the fence of being dangerous.

The black widow is one of the first spiders to come to mind when one considers dangerous United States spiders. This nasty little bugger can actually kill you if you are susceptible to spider bites. Any bite is serious, and should be treated immediately. The elderly, children, and people in poor health are the most likely to suffer extreme cases. All people that are bitten are in danger and should go to the hospital.

The black widow is generally easy to identify, though some things can throw you off. As a rule, the black widow female is the one that you should be most concerned with. It is about the size of quarter, and has a round, bulbous belly.

The black widow is famous for the red hourglass that is found on the belly, but this should not be all inclusive. The hourglass can be red or even orange in color. The hourglass can also be anything from a stripe to a dot, to a series of dots. This depends on age, as well as the location of the spider.

Color of the black widow is also something that can really confuse people. By and large, they are shiny dark black in color. They can also be slate grey, brown, or any other shade of black.

The black widow produces a drunken web, that tends to be highly irregular in shape.

The brown recluse is the second spider in the United States that you have to be aware of. This spider is highly dangerous if for no other reason because they are often found around the house.

They also have a necrotic bite. That is, the bite will eat away the tissue around the bite site. A bite from the brown recluse has caused amputations and has the same risks as the ones mentioned above for the black widow.

The brown recluse, or fiddleback as it is sometimes called, can be identified by the violin shaped marking on its head and back. The neck of the violin points towards the back of the spider. The brown recluse has a uniformly colored belly that is like a long circle.

The color of the brown recluse is actually varialble as well, but most commonly brown. This spider can also be light brown, tan, or even almost white in color. Another telling feature of the brown recluse is the fact that they have six eyes rather than the eight normally found on spiders. These six eyes are arranged in pairs of two. Two in the middle and two sets on either side.

Tarantulas - Several species of tarantula have very painful bites and can be found in the United States. Some are indigenous to the United States, and some are brought in as pets. Tarantulas are generally large spiders, that are covered in hair. This also gives the tarantula a large set of fangs that are no fun to be bitten by. Most tarantula venom is not particularly dangerous to humans, but bites shoud be treated.

Wolf Spiders - The wolf spider is a burrowing spider that is non-aggressive in nature. The union jack symbol is generally clearly on its back. This spider has a painful bite, but not a particularly dangeous one.

Mouse spiders - Many people are not familiar with this particularly painful spider bite. It is actually comparable to a red-back spider in toxicity, and should be treated right away if bitten. The mouse spider is known for a bright red head in the male, with prominent large fangs.

Hobo Spiders - Very comparable to the mouse spider in that people do not know much about them. They are dangerous to a degree and should be treated immediately if bitten. The hobo spider is often marked with chevron patterns on the abdomen. They are about brown with about a two inch leg span.