Do all spiders bite?

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!