We are always asked how to tell the difference between a harmless and dangerous spider. Which spiders are poisonous are which are not? Well, here it is. A quick and easy reference guide to the four arachnids to avoid in Southern California. Print it out, stick on your fridge, bulletin board or keep a handy copy on your phone. Know how to spot a poisonous spider and know what to do if you or your children are bitten.