Harlequin Poison Frog

A Living Warning Sign

The Harlequin Poison Frog (Oophaga histrionica) does not try to hide: it forages by day, relying on its warning colours. It measures only 2.5 to 3.8 centimetres long, and the AnAge ageing database records a maximum lifespan of 9.1 years in captivity. First described in 1845 as a bright orange frog with black web markings all over its body, it turned out to vary far more than that. Animal Diversity Web’s 2001 account lists base colours of orange, yellow, red, white and powder-blue, with some colour forms varying from valley to valley. The black webbing ranges from thin stripes to speckled, broken lines to an all-black frog with a few coloured spots. The same account says the bright markings probably act as a warning to potential predators.

Borrowed Poison

The frog does not make its toxin from scratch. Animal Diversity Web says it collects the toxin from its prey, mainly ants, termites, small beetles and other small arthropods in the leaf litter, and deposits it in its skin. The result is a highly toxic poison capable of repelling or even killing small predators, and potentially dangerous to people who handle the frog.

The “poison dart frog” name is borrowed too. Poison frogs are often called that because the Chocó people of western Colombia tip blowgun darts with frog toxin, but San Diego Zoo Wildlife Alliance names one species as the frog they use, the golden poison frog, and says scientists know of only three frog species used for darts.

A Jammed Nerve Signal In poison dart frogs, Animal Diversity Web says, the skin toxin blocks nerve signals at the acetylcholine receptor of the neuromuscular junction, the switch nerves use to fire a muscle.

A Mother’s Borrowed Nursery

Breeding runs through the rainy season. A male calls from a perch with a trilling buzz to draw in a female, and once paired, she lays her eggs on the surface of a leaf while he follows behind and fertilises them. She stays by the clutch to guard it. About ten days later, the tadpoles break free of the jelly-like egg mass and swim onto her back using their tails, and she carries them one at a time to a separate pocket of water, usually pooled in a bromeliad’s leaf axils. The tadpoles are obligate egg feeders: she returns every other day to lay infertile eggs in the water for them to eat. After three months of metamorphosis, the young frog climbs out of the bromeliad to start life on land.

One Frog, At Least Five

Animal Diversity Web’s 2001 account placed the harlequin poison frog in rainforest from western Ecuador north through Colombia’s Chocó region, but that single-species picture turned out to be too simple. A 2018 study combining genetic, morphological and ecological data across the histrionica complex found at least five species inside it, three of them new to science, some in small isolated populations outside any protected area. Its authors wrote that some of these species should be considered among the most vulnerable frogs in the Neotropics. The IUCN lists Oophaga histrionica itself as Critically Endangered, assessed in 2019.