How can you tell if a spider is poisonous?

Question

Are most spiders harmless?

Answer 1

all spiders have venom, let me make that clear right now. (harvestmen / daddylonglegs aren't true spiders and are completely harmless)

that said only a few types of spiders are actually dangerous to people/ the blackwidows/ redback spiders are one of the more dangerous specimens. the brown recluses are another example , and the sydney funnel webs are also dangerous.

other than those ones almost every other spider is either harmless (its fangs can't pierce human skin) or at least not dangerous (it can pierce skin and inject venom but the venom is either too weak, or not enough to cause any troubles).

the majority of spiders are completely harmless and even beneficial since they eat pesky insects. ironically the biggest spiders are relatively harmless. tarantulas bite is about the same as a bee sting, but with a tarantula you get bit once, and don't have to worry about a swarm of them chasing you.

most spiders you find are harmless though. brown recluses have a violin shape mark on their backs.. black widows are very black and have the hour glass mark, redbacks look just like a black widow but have a red patch on their backs instead of an hourglass on their tummies. a sydney funnel web is quite a big spider and if one of them crawls up to you you'll know it, but unless you live in sydney you don't have to worry about them.

if it spins a nice orb web, it is most likely harmless.

that said it is still a good idea to not handle spiders with your bare hands. you could be allergic to its venom, or you could misidentify one. but if there is some spider making its home in your house, leave it alone unless it is bugging you.

Answer 2

First of all, spiders aren't poisonous, they are venomous.

The only way to tell if a spider is venemous is to identify it. Some spiders, like brown recluse, have an acid-based venom that eats your flesh. (It happened to my leg, it's lovely)
Banana spiders will just make you feel like you have the flu. They are beautiful though.
Black Widows will make you really sick, and can kill a small child.
There are several other types of dangerous spiders, the best thing to do if you have been bitten and can catch the spider is to have a professional identify it and treat you accordingly.

Answer 3

While MOST spiders are relatively harmless & help control insects, the majority of spiders have venom to one degree or another.
Some spiders have venom that is fairly innoccuous to humans, even if bitten. Their venom is primarily an aid in helping them to disable their intended meal.
However there are enough spiders that have venom that is very potent, & potentially life threating to humans who are unlucky enough to be bitten.
The watchword for the day for the average person is to take necessary E.P.A. approved chemical precautions in your home, attic, garage, & outbuildings.
If you have areas where children must play, then this is precaution that must be taken in these areas also.
Unless you are a trained entymologist, you really have no way of identifying which of the little beasties MIGHT be the one to be the most dangerous to you.
The innocuous & little noticed Brown Recluse is a good example. You do not want to bitten by them under any circumstances.
The primary reason is that NO ONE has any way to predict how their body will react to any venomous bight.
Example: I am not prone to any severe reaction to bites except the normal reaction to the bite of venomous snakes but my wife, (a very healthy person in all respects), is so allergic to Bee Stings, that she is supposed to carry a PIN with her at all times. We came within minutes to losing her to anaphelectic shock many years ago.
My Brother served two terms in Combat in Vietnam where there is some of the most dangerous snakes in the world, as well as extremely venomous insects. But the closest he ever came to death was his reaction to a Black Widow Bite when he was about 12 or 13.

Answer 4

They're all poisonous, but most are harmless. And no, you can't tell the potentially dangerous ones from the completely harmless ones unless you already are familiar with the species -- there are no telltales which say "I'm deadly!!"

My boss assumes that every spider he comes across is a brown recluse, and promptly stomps it. He's wrong 99.99% of the time.

Answer 5

It depends on where you live. Being in NY, I don't have to worry about poisonous spiders (thank God). Someone living in say, Texas, might have to. Consult a book from your library on spiders to find out if you have to worry

Answer 6

Most spider are venomous, but this is like most anything else, it is a question of dosage.
Of all the venomous spiders, only a tiny percentage have a venom that is strong enough to be dangerous to humans.
To tell which ones are, I guess you have to know how to recognize all the dangerous ones, and that knowledge probably came from some infortunate people who did get bitten.

Answer 7

I've heard that the daddy long legs spider is the most poisonous spider, but it's because it's mouth is too small to bite us that makes it harmless.

Answer 8

All spiders are poisonous. It just depends how strong their poison is against us. Whey would they be able to harm a small defenseless fly, but not us? Think about it.

Answer 9

^Simple if it bites you and you get sick and/or die it's poisonous, well actually venomous. lol

Seriously, there are many that are harmless and quite a few that can be deadly, the first site below will show you pictures. The only way to know, is if you know what they look like. I know this sounds trite but it's true.

Answer 10

ACK! Poisonous or not I would never eat a spider!