From Scientific American:
The poison frogs of Central and South America are as deadly as they are beautiful, thanks to chemicals called alkaloids that they secrete through their skin. Indeed, the venom from a single golden poison frog, for example, can kill 10 humans. Now researchers have unlocked the secrets of their counterparts in Madagascar and found that they employ the same method of acquiring thier toxins: through careful food consumption. Studies of frogs in the Neotropics indicated that a diet rich in ants provided the alkaloids.