Why do spiders bite humans?

Throughout my life I’ve had dozens of spider bites, most of which occurred while I was sleeping. But why do they bite in the first place?
My understanding is that spiders paralyze their prey, and the venom turns the insides to mush, which the spider then sucks up. But there is no way, even if they looked at us as a food source, that they could turn our insides to mush. So that can’t be it…
Perhaps they bite us because they are fearful of us, you say? Out of all the bites I’ve had, I don’t think I’ve ever felt a single one. I’ve never woken up due to the pain, nor have I swatted one on my leg in the process of biting me. So it can’t really be for protection either, because if I don’t feel the bite, it won’t make me go away. I only notice the bite when it starts to itch.


Wistful thinking? You know how long we would feed a spider for?


So, what makes you think you were actually bitten by a spider?

Obligatory link.

First, I would question whether they are really spider bites. It’s pretty well established that people blame spiders for all kinds of things that are clearly not caused by spiders. For example, I’ve never heard of a spider bite itching as you describe.

Second, if you roll over on a spider while it’s crawling around at night it is going to react instinctively without giving the matter any thought whatsoever. If that instinctive reaction is to bite first and ask questions later, that’s what will happen.

They want your drugs.

SDSTAFF Doug has written staff reports about real and suspected spider bites. See this one, for example: http://www.straightdope.com/columns/read/2235/my-dads-hospitalized-with-a-big-bump-on-his-arm-could-it-be-a-spider-bite

Exactly what I was thinking of.

I wonder why there are no spiders that prey on animals they don’t kill? Some insects have anesthetic bites, so the ‘prey’ doesn’t know it’s being bitten. Why not a spider that bites painlessly, turns a little of the (possibly sleeping) host into soup, and drops away before it’s discovered?

Because they hate our freedom.

According to Neil Gaiman (Anansi Boys), spiders do this because they think it’s funny. :smiley:

Made me giggle out loud.
But shouldn’t that be “our precious freedoms”?
Anyway- good one.


These arachnids exist (almost - they eat the soup that’s already there)

We call them ticks.

When I was about 12 ,I was a live and let live guy. I saw a 1/4 inch fuzzy brown spider climb on my hand. He slowly walked up the arm. Then when he reached right above my elbow ,he gave me such a bite. It hurt like hell. I ran to the bathroom and then ran cold water on it.
Then I went back to the front room looking for him. He was going to die. He declared war , I didn’t. Since then small brown fuzzy spiders must die.
I don’t think he was planning on eating me. I presented no threat. He was just a prick spider who is responsible for the death of a few brown spiders.

Itching bites are generally produced by things like mosquitos, biting flies, bedbugs, etc. It’s a histimatic reaction to the anesthetic they use. Venomous bites (spiders) produce pain and generally have visible double fang punctures in the center.

Random infections can produce swollen, painful lumps. I got one on my upper lip once. I had a tiny zit that I hit with my razor. There wasn’t even any blood to speak of. 72 hours later, it looked like Mike Tyson punched me in the mouth and I was getting huge cocktail antibiotic shots because the bacteria was resistant to standard antibiotics. Scary.

Remember, all bugs have bacteria living on their little fangs capable of producing an infection. As well as splinters and anything else that can puncture skin.

If a tiger pounced on you, would you not punch and kick at it? The chances of your attacks doing anything are negligible but you’re still probably not just going to lay there and let it eat you.

A friend got nailed by a Brown recluse. It was ugly with skin atrophy around the bite. As a bonus it would flare up every couple years and look like it had bitten him again. It was ugly and returned sporadically for over 10 years.

My wife would argue it’s because they are evil Satan spawn. (She’s scared of spiders)

On the original post: as has already been pointed out, probably few if any of your “spider bites” are spider bites, or indeed the bite of anything. If you don’t see any biting organism, don’t be so quick to assume it’s a bite: some of the non-bite conditions can be serious, occasionally even life-threatening! See my page on the topic, also these:
for answers to the question “what else could it have been?”

The idea that spiders bite people who roll over them in their sleep is also a myth. Spiders’ fangs are on the underside of the spider. The reflex bite that occurs when the spider is being crushed to death by an enormous monster rolling onto it, will be delivered to the sheets, not to you, in the vast majority of cases.

The idea that you can recognize a spider bite by 2 punctures is also a myth (click link for my page on the topic).

If your friend didn’t live in the green area on this map, then what he got nailed by was medical malpractice. See some of the articles linked above, also this one and my page on the subject. This is one area about which 95% of physicians know almost literally nothing - because they get nothing significant on spiders in medical school. So they do what everyone else does, and blame all mysterious skin lesions on unseen spiders.

Patially true, depending upon which spider we are referring to.

Large spiders, such as some of the wolf spider varieties I’ve dealt with, will ideed leave visible fang marks. I know from experience. I was in the military and had a lot of field time with spiders capable of carrying off full grown locusts while running. These roaming hunters are also fairly agressive and will bite quickly. Their size also means they leave a sizable swollen painful lump. Common house spiders on the other hand would probably have a hard time penetrating skin with their tiny fangs. For those who live close to wooded areas, larger spider pests entering the house are pretty common.

Certainly it is possible for a large spider (or one with large fangs, like the woodlouse spider) to leave visible puncures, but even in the largest spiders it occurs no more than half the time. I myself have been bitten by a large tarantula (one of the 2 genuine spider bites I’ve ever had, after handling tens of thousands of live spiders) and the punctures were very hard to detect.

The idea that smaller spiders cannot penetrate the skin is yet another spider myth. It’s not that they can’t, but that they very rarely do because they have no reason to.

The idea that large spiders in the house must have entered from outside is still one more spider myth. And with rare exceptions like the brown recluse (found only in a limited area, despite all the foolish rumors claiming that it’s found everywhere), house spiders are not pests. They are beneficial - they EAT pests!