How do you tell if a caterpillar is poisonous or venomous?

Throughout the animal kingdom, animals that are poisonous benefit from advertizing this fact because they are then less likely to be hunted and eaten. Usually they have bright colors like red and black. This is their way of letting us know that they are dangerous. What do you think of when you see red? I see "STOP". How about when you see black? I see "DEATH" Even the animals such as a frog that is green and black. Green for me says "GO" but then it has black so I know that if i do go and touch it it may cause death. Animals help us understand that they are either poisonous or not.

It is hard to tell, the best thing is to be careful, ask an expert, or find a good reference book.