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(Harlequin Poison Frog)
There are around 180 species of frogs that have the ability to produce extremely poisonous skin secretions, and these are called poison frogs, or dendrobatids.
All frogs actually produce poisonous skin secretions; however, humans do not notice the toxicity or suffer skin irritation when handling most species. But in the case of dendrobatids, their alkaloid skin secretions can be lethal to humans if absorbed through mucous membranes or passed through a cut on the skin. For example, a single golden poison frog harbours enough poison to kill 10 grown men, making these frogs perhaps the most poisonous animals alive.
How do these poison frogs make these toxins? It’s not completely clear, but at least in some dendrobatids, it seems to be derived from their consumption of beetles. What's more, it's not just adult frogs that are poisonous. Tadpoles are too. The mother frog supplies their tadpoles with poison by feeding them their own unfertilized eggs. The tadpoles then absorb the toxin and become poisonous themselves.
You might be thinking, what use is this? After all, by the time the predator is harmed by the poison, the frog would have been eaten too. This is why poison frogs have a warning system in place to deter predators: colour.
Poison dart frogs are brightly coloured, including colouration of white, black, yellow, orange, red, green, blue and everything in between. In nature, bright colours are often a warning sign that the animal is poisonous. This is called aposematic colouring, and it warns predators that the animal is dangerous to eat. Some animals take advantage of this system; they boast bright colours yet pose no danger. However, poison dart frogs aren’t bluffing. Their poison really does pack quite a punch.
Sources:
https://www.nationalgeographic.com/animals/amphibians/group/poison-dart-frogs/
https://nationalzoo.si.edu/animals/poison-frogs
https://www.britannica.com/animal/poison-frog
Photo credit: https://www.britannica.com/animal/poison-frog