All spiders have venomous bites.
While most spiders avoid humans and only attack as a last resort, all of them do have venomous bites. The reason some spiders are deadly while others are harmless is two fold.
One, it depends on the strength of their venom.
Some spiders have very very toxic venom like the black widow or brown recluse that can cause serious tissue damage and even death to us humans. Others have less toxic venom, to humans that is! It all depends on how toxic a venom each spider needs to kill it's food. Since we are not on the average spider's diet, most of them don't need venom strong enough to kill us.
And second is the strength of a spiders jaws and "fangs".
Some spiders are just not strong enough to pierce our tough skins!
Answer by AAA_Webmaster
I know some spider bites can kill you while others are harmless. But do they all bite? Do they all have venom?
There are not any stinging spiders are there?
Charlotte may have weaved "some pig" into her web to help Wilber get to the fair but some Australian scientists are finding that many of the beautiful patterns and crosses we see in spider webs actually have a less then asthetic value.