This all depends on what area of the world you live in. In the U.S., some dangerous spiders include the Black Widow spider. A bite from a black widow can cause serious illness and even death. There are two types...they both have an hourglass design on the back of their fat, bulbous bodies. The ones with the red hourglass can hurt, but their poison is nowhere near as potent as that of the yellow backed black widow, which can cause death. DON'T quote me on this though...some people say that the color makes a difference, but many more people say that it doesn't matter...BOTH are poisonous. Typically, a bite from either one wouldn't really be deadly unless you were allergic to them, or if you incur more than one solid, venomous bite. Regardless, you should always be aware that Black Widows are dangerous. Black Widows are found all throughout the United States, though the more venoumous ones tend to occur in the Mid to SouthWestern US. Brown Recluse are not household spiders...they live outside under rocks, leaves and twigs. They are brown, large and hairy with bulbous bodies. Hence the name 'Recluse' they will only attack when their home is disturbed. Brown Recluse ARE dangerous, and their bites can cause death. They are quite prevalent on the east coast of the United States, particularly the Mid-East Coast, from pennsylvania southward to Florida. Wolf Spiders are vile looking spiders that have elongated bodies and visible fangs. They have long, stick-like legs and can run quite fast. They often make their way inside a house during the summer months. Their bites are not deadly, but can cause a serious sting. They are located throughout many areas of the U.S. Your common variety Garden Spider is a rather ungainly looking creature...at first glance it appears to be a small tarantula, with a hairy black body. Their bites can cause serious pain and swelling, and if left untreated can cause painful infection. They are often found in grass and gardens and other wooded areas, and make their way into the house during warmer months. They, like many other spiders, have the ability to make their bodies go completely prostrate and flatten themselves to fit into VERY tight spaces...I once had a horrifying encounter with one when I opened up a dictionary that had been sitting unused downstairs for a few years, and the ugly little wretch sprang out. In the Midwesern and South Western united states, you have tarantulas of various sizes that can cause serious pain and infection with a bite. Desert Tarantulas are particularly bothersome and make their way towards houses whenever they feel like it. They don't usually make their homes inside houses unless you have a cellar. They will usually find a dark, moist area in the cellar to set up home. They'll take care of your mouse problem, but will also be a potential threat to young children and pets. They may also reside in your attic if they can find a way up there. You can easily identify a tarantula: a large, vile looking arachnid covered with hair. They usually grow to be larger than the palm of your hand and can vary in speed. If they are threatened, they will rear up their fore legs to appear larger. Try not to kill them if you find one in your house...just try to get a net over it or capture it in a jar and toss it outside...it'll probably go away. If you decide to squash it, you'll have a heck of a mess on your hands to clean up. Jumping Spiders (I don't know their class name) are not very dangerous, but can be identified by their thick, bulbous bodies and rather short legs. They move very quickly...and can leap far distances. They very rarely bite, and if they do bite its nothing more than an unpleasant sting. But it is a common spider in the house. There are many other types of spiders that make their way into the house, and you can find out more by reading up on them on many websites. While I don't know of any off the top of my head, you can run a search of 'household spiders' and come up with quite a few. Side note: Julia Gregory, PLEASE don't give answers negative ratings simply because you think you know more...i'm not an expert in spiders in any way whatsoever, but when it comes to many venomous spiders, and particularly Brown Recluse, I know what I am talking about and i'm only stating things I know as FACT. If you feel that you can contribute to this question, then do so by submiting your own answer. Don't abuse the rating system by marking my answer wrong to make snooty comments or 'correct' me when i'm not wrong at all. Be in full possession of facts before you mark other users' answers wrong. The website you placed in your comment even supports my original answer.

There's actually another dangerous household spider. It's called a Hobo spider. It's a fairly large spider, and the two palps have swollen knobby things on the end of them, making them resemble little boxing gloves. This is what the male Hobo looks like. The female is quite similar, only without the gloves. Her cephalothorax is fatter also. For actual pictures of them, go to http://www.hobospider.com/info/index.html From what I read on this site, they're fairly aggressive (for spiders.) This site also has pictures of the Brown Recluse, which also has a nasty bite. Hope this helps :D

There are a bunch of "recluse" species of spiders, but it is the "brown recluse" which has been most studied. This poisonous spider is found in the south central midwest. (Texas, Kansas, Tenn, Kentucky, Mo., Alabama areas) It can be common to find this spider in homes, like Julia Gregory said. I live in Texas also. All the recluse species have six eyes instead of the typical eight for spiders (if you want to get that close...ha!) Markings will vary depending on species or the age of the recluse spider, but there is a lot of misidentification and confusion as to the brown recluse. Adult brown recluse can have a very small, dark violin-shape contrast near the front, while the rest of the body is a lighter brown. Actually, some non-recluse species can have a kind of a violin marking (typically on the west coast). There are a lot of "brownish" spiders and so the confusion can go on and on. The brown recluse is said to vary in size from a dime to a quarter. They tend to be shy and often hidden. There are many stories told of the outhouse brown recluse bites. Again, there are different species of "recluse spiders" and so confusions can develop about the brown recluse. This violin shaped dark "shadow" is a real key in recognizing the brown recluse. There are two main portions of the body, front and rear. The violin shape is on the front portion with the neck of the silhouette pointing towards the rear (abdomen). The base of the violin ends at the head of the spider. When one is bitten by a brown recluse, there may not be an immediate pain. Later (a few hours) it could become swollen, red, etc. With some people sometimes the area gets worse and worse. With others there may not be much of a reaction. Symptoms can vary with an individual. Ideally, if one is bitten by a spider, capturing it "dead or alive", would be helpful if medical treatment is needed. Misidentification is common, so a sample will surely help. There are some things that a person can do to inhibit spiders within the house. See the "pest control" area of this website.