Poison Dart Frog

Poison dart frogs are small, jewel-bright rainforest amphibians that broke one of nature’s usual rules. Most animals hide. These frogs advertise — because they are, or may be, deadly to touch.

Overview

“Poison dart frog” covers around 200 species in the family Dendrobatidae, found in the rainforests of Central and South America. They live on and near the forest floor, active by day, hopping through the leaf litter hunting tiny prey. Their colours range across the entire spectrum, and pattern often varies even between neighbouring populations of the same species.

The poison

Poison dart frogs do not make their own toxins. They sequester them — extracting alkaloid compounds from the ants, mites, springtails, and small beetles they eat and concentrating them in glands in the skin. Frogs raised in captivity, or wild frogs moved to a new diet, gradually lose all their toxicity, and their offspring are born harmless.

Toxicity ranges from barely noticeable to extreme. The golden poison frog (Phyllobates terribilis), a 5-centimetre frog from a small patch of Colombian rainforest, is among the most poisonous animals alive: its skin carries roughly a milligram of batrachotoxin, which locks open the sodium channels in nerves and muscle, causing paralysis and heart failure. That is enough to kill ten or more adult humans, and there is no antidote.

Bright colours as a message

The vivid colouring is aposematism — an honest warning. Predators that eat a toxic frog and survive learn to associate the colour and pattern with sickness and avoid it afterwards, and some non-toxic frogs and insects mimic dart-frog colours to borrow the protection. Only a single snake, the fire-bellied snake Erythrolamprus, is known to be able to eat the more toxic species.

Parenting

For such small animals, poison dart frogs are unusually devoted parents. A female lays a small clutch of eggs in moist leaf litter, and one parent — usually the male — stays to guard them and keep them damp, sometimes urinating on the clutch to stop it drying out. When the eggs hatch, the parent lets the tadpoles wriggle onto its back and carries them, one or a few at a time, up into the canopy to deposit each in its own tiny pool of water held by a bromeliad plant. In some species the mother then returns regularly to lay unfertilised eggs for the tadpoles to eat.

Threats and conservation

Individual species range from Least Concern to Critically Endangered; the golden poison frog is Endangered. The pressures are those facing amphibians everywhere:

• Deforestation for logging, agriculture, and coca cultivation, which destroys the specific patches of forest many species are confined to.
• Chytrid fungus, a skin disease that has devastated amphibians across the Americas.
• The pet trade, which historically stripped wild populations, though most frogs sold today are captive-bred.
• Climate change and pollution, to which thin-skinned, moisture-dependent amphibians are especially sensitive.