Why don't poisonous animals poison themselves?

THERE WOULD BE LITTLE POINT IN having the ability to lethally poison a predator if you accidentally poisoned yourself and ended up just as dead. In the case of poison dart frogs, they dodge being poisoned twice in the process of protecting themselves. Initially, the frogs ingest a toxin from the ants, mites and centipedes they consume, which have been eating poisonous plants. Though research on the subject is ongoing, scientists believe the ant toxins don't harm the frogs because of a protein in their gut, which is released as the ants are digested and interacts with the poison.

- Sheena Harvey

Essentially, this protein binds to the toxins and carries them through the frog's bloodstream to the skin, where they end up in structures known as granular glands. These glands produce secretions full of the acquired toxins and coat the frog's skin: the process is rather like wrapping up the poison molecules in tiny bags and shipping them to a distribution centre before they can do the frogs any harm.