Frog skin is often smooth and wet. The skin of some types of frogs also happens to be extremely poisonous. Now, scientists say they've discovered one of the major sources of this poison. It comes from ants that the frogs eat.

Frogs have an enormous variety of chemicals in their skin. Depending on the chemicals present, some species simply taste bad. Others are so toxic that they can kill animals that eat them.

Scientists had guessed that frogs make their own toxins. Most frogs raised in captivity, however, aren't poisonous unless the food that they're fed contains toxins.

John Daly of the National Institute of Diabetes and Digestive and Kidney Diseases in Bethesda, Md., was particularly interested in a group of about 80 poisonous chemicals called pumiliotoxins. These chemicals show up in the skin of certain tiny frogs from Madagascar and from Central and South America.

Daly and his colleagues collected about 500 samples of insects and other little creatures from eight sites in Panama. The only pumiliotoxins they found among these critters were in formicine ants. The subfamily of formicine ants includes carpenter ants and wood ants.

The scientists found the same types of ant inside some poison frog stomachs. The frogs apparently steal the poison from the ants to use for their own protection.

Frog legs, anyone?—E. Sohn