The skin of Madagascar poison frogs contains the sugar sucrose — the first known case of sucrose produced by an animal, and not a plant.
The sweetness comes with a deadly kick, though, since these frogs also contain poisons in their skin, hence their name and bright coloration that helps to warn off potential predators.
Herpetologist Valerie Clark of Queen's University in Belfast and her team made the discovery while analyzing the chemical secretions of Madagascar poison frogs (Mantella) and certain Neotropical poison frogs (Epipedobates, Dendrobates).
Clark and her team believe the froggy sweetness was gleaned indirectly through their diet. In this case, you can definitely say these frogs are what they eat.
Frogs aren't eating candy all day, of course. They dine on ants. In fact, over half of the more than 600 contents identified from Mantella stomachs were ants. Most of these ants, in turn, live close to, and are cared by, frogs. The ants come from the superfamily Coccoidea. (You can read all about that unusual close relationship here.)
These ants acquire sugars from the sap of their host plants, so the sugar goes from the plant to the ant and then to the frog, which secrets it out of its skin. The function of the sugar there remains a mystery.
Clark and her colleagues also found that Madagascar poison frogs secrete tauromantellic acid, a bile acid. This is the "first example of a genuine poison frog metabolite from the skin of any tropical poison frog," the authors write in their study published in the Journal of Natural Products.
They continue, "It is interesting to speculate on the reason for the presence of this unusual bile acid in poison frog skin, and it is possible that this compound plays a key role in sequestering alkaloids and protecting the frogs from their own toxicity."
The researchers go on to explain that this probable protection likely happens through various chemical reactions with other substances.
Clark is sometimes known as "the frog licker" because she often does just that. But she's quick to add that "I don't recommend this because if you lick the wrong frog it can be very bad."
Sugar or not, it's therefore not wise to lick a Madagascar poison frog. Leave it to the pros like Clark, profiled in the below video.