Amphibians
Smoky Jungle Frog
Leptodactylus pentadactylus · also called South American bullfrog, smoky frog, rana ternero
The smoky jungle frog is a heavyweight of the rainforest floor — a frog the size of a dinner plate that eats other frogs, snakes, and the occasional bat. Pick one up and it screams like an injured animal while coating your hands in burning slime.
Overview
Leptodactylus pentadactylus ranges from Central America across the Amazon basin, in lowland rainforest. Large females reach 18–20 cm and 250 g, making it one of the biggest frogs in the Americas. Its smoky brown, blotched colouring hides it in the leaf litter, where it ambushes almost any animal it can swallow.
A loud, slippery defence
Its first defence is stillness. Grabbed, it screams — a piercing distress call likened to a cat or a hurt child — and its skin floods with irritant, toxic mucus that makes a predator gag and a handler sneeze and itch.
Nests of foam
The pair whips mucus and jelly into a floating raft of foam in a rain pool or burrow. The eggs and young tadpoles develop inside it, sheltered from drying and predators. The tadpoles are large and cannibalistic.
Status
The smoky jungle frog is Least Concern and common across a huge range. Its Caribbean cousin, the mountain chicken, is Critically Endangered.
Smoky Jungle Frog: common questions
Why does the smoky jungle frog scream?
It is a last-ditch defence. The frog's first line is camouflage and stillness; if that fails it inflates its body, lifts itself up, and may lunge with its mouth open. If a predator actually grabs it, the frog gives a sudden, very loud, high distress scream. The noise startles many predators into loosening their grip for a fraction of a second, which can be enough for a powerful frog to kick free, and it may also attract a larger predator that will interrupt the attack. Combined with the slippery, foul mucus flooding the predator's mouth, the scream gives the frog a real chance of escape even after being caught.
Is it dangerous to handle?
It will not seriously hurt a healthy adult, but it is unpleasant and best avoided. The skin secretions are irritant and mildly toxic; people who handle smoky jungle frogs report sneezing fits, watering eyes, and an itchy or burning rash on the hands, and the effects are worse if the secretions reach the eyes, nose, or mouth or an open cut. A large frog can also deliver a surprisingly hard bite. The main reason to leave it alone, as with any amphibian, is that human skin oils, salts, and any residue of soap or repellent are harmful to the frog.
How does a foam nest work?
During mating the male and female use their hind legs to beat a mixture of mucus, fluid, and the jelly around the eggs into a stiff foam, rather like whipping egg whites. The foam is laid in a shallow rain pool, a flooded burrow, or a depression the frogs excavate near water. Inside, it stays moist, cushions the eggs, holds oxygen, and hides them from predators and from the sun, and it contains compounds that resist bacteria and fungi. The eggs hatch within the foam, and the young tadpoles feed there for a time before rain washes the nest into open water or the tadpoles wriggle out themselves.
Is it the same as the mountain chicken frog?
They are close relatives in the same genus, Leptodactylus, and both are very large, powerful, foam-nesting frogs, but they are different species from different places. The mountain chicken is Leptodactylus fallax, restricted to the Caribbean islands of Dominica and Montserrat and now Critically Endangered, historically eaten as a delicacy. The smoky jungle frog, Leptodactylus pentadactylus, is a mainland species ranging from Central America across the Amazon, and it is common and not threatened. The smoky jungle frog is sometimes called the South American bullfrog, which adds to the confusion.