Why are some frogs poisonous?

Not all frogs are poisonous but some have developed a venom that they can use should they come under attack from predators. The common toad contains a poison that it exudes through its skin if attacked. Dogs and cats commonly experience this poison, however they seldom suffer serious effects. It does teach them,however, to avoid these amphibians. Cane toads are very large toads which contain a drug capable of causing hallucinations if eaten. The skin of some frogs and toads contain poisons which are among the most powerful known to humans.

Fact:
The South American arrow frog is extremely poisonous. It advertises this danger by being very brightly coloured.

(1) Blue poison arrow frog (2)poison arrow (3)Yellow-headed Poison Arrow