Where is the poison dart frogs poison?

Most species, and there are several, release an alkaloid toxin through their skin.

They do not synthesize their own poison but store chemical toxins from some of the insects they eat like ants and termites. This is good since it means that many captive frogs do not have sufficient levels of toxin to harm their owners.

It is the secretions of the skin of the poison dart frogs that is toxic. All the frogs of this family "borrow" toxins from what they eat that actually makes the toxins (mostly ants and mites) because the frogs themselves don't manufacture the poisons. These toxins, a few of which can be quite dangerous, are "worn" by the frogs for protection.