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Poison dart frogs live on the ground or in the trees of moist tropical forests. They are one-half to three inches long and brilliantly colored in wild stripes and spots. They eat insects, including termites, ants, flies, and crickets, which they catch with quick flicks of their sticky tongues. They are occasionally preyed on by snakes, birds, and human beings--but they have excellent defense mechanisms against predators.
Poison dart frogs are among the deadliest animals
on Earth. Their skin contains glands that produce toxins. The
primary ingredients for frog toxins are alkaloids that come from
rainforest plants. Dart frogs eat insects that eat plants containing
alkaloids. Other animals that make the mistake of eating poison
dart frogs get sick and may die.
Dart frogs bred in captivity are not poisonous. Their primary diet is lab-raised fruit flies, which do not contain ingredients necessary for the production of toxins.
Warning Coloration. How do predators
know not to eat poison dart frogs? Dart frogs send a WARNING.
Their brilliant colors--red, purple, yellow, and blue--warn hungry
predators that they taste BAD. Some animals know instinctively
not to eat anything brightly colored. Others learn through experience
that eating dart frogs will give them terrible stomach aches.
Warning coloration is shared by other amphibians and many insects, including the blue morpho butterfly.
Most frogs are nocturnal (awake and active at night), but poison dart frogs are diurnal (awake and active in daylight). This may be in part because their warning coloration is more visible in light, protecting them from predators as they go about their business. They are bold creatures, unafraid of being eaten by other animals.
Look out, little frog! One snake--Leimadophis epinephelus--is immune to dart frog toxin.
Can a Dart Frog Kill a Human Being?
A few species of poison dart frogs do contain enough poison to
kill an adult human being. But the toxin has to get into a person's
bloodstream to work. Rainforest natives know not to eat dart frogs
or to touch a frog and then touch their own eyes, noses, or mouths.
Poison dart toxins can easily seep into capillaries in the delicate
membranes that line eyelids, nostrils, and mouths.
Dart frog toxins affect the nervous system, causing convulsions, muscle spasms, and paralysis. If the poison is strong enough, breathing and heartbeat stop.
The most toxic dart frog is Phyllobates terribilis, a species found in Columbia. A single terribilis may contain enough toxin to kill 100 human beings--which makes it 20 times more toxic than other dart frogs.
Why Are They Called Poison DART Frogs?
The Choco and Embre Indians of western Colombia use the toxic
secretions of dart frogs on the tips of their small spears and
blowgun darts. Usually they skewer a frog and roast it over a
fire. Or they may toast a frog like a marshmallow on the dart
itself. As it cooks, the toxic mucus oozes out of the skin as
a white froth. Toxin from one frog may coat up to fifty darts
and will last for as long as a year.
Indians use poison darts to kill animals for food because they are an efficient way to bring prey down from the rainforest canopy. In the past, they also used them as weapons in warfare.
How Do Dart Frogs Reproduce? Male poison
dart frogs are territorial. They stake out a small area on the
forest floor and wrestle with other males to protect it. They
buzz and chirp to attract females into their territories, forcing
air from their vocal sacs through slits in the backs of their
throats. (Only male dart frogs have vocal sacs.)
Dart frogs mate and lay eggs during the long tropical rainy season (usually about six months). Each female lays two or three sets of four to ten eggs under a rock or log, on a leaf, or in a small pool of water. Male frogs fertilize the eggs externally. The fertilized eggs are protected with a thick jelly-like substance. Each is a semi-transparent sphere, within which the developing tadpole is clearly visible.
Metamorphosis. Poison dart frogs are
amphibians, which means that they have "double lives."
They hatch as tadpoles, little aquatic animals that breathe water
through gills. As they mature, they undergo a profound change
to become frogs that breathe air through lungs. This is called
metamorphosis.
Tadpoles look a little like fish, with big heads, long tails, and no legs. When metamorphosis begins, they start to grow four legs and their tails become shorter. While this is happening, their internal organs are changing. They are developing lungs, and their gills are beginning to disappear.
After many weeks, the tadpoles' legs are fully developed and their tails have been absorbed into their bodies. In just a few more weeks they reach full maturity as little frogs. Complete metamorphosis takes twelve to sixteen weeks.
The Cuban poison dart frog is the world's smallest at 1.3cm. Unlike other frogs, it lays only one egg and skips the tadpole stage, emerging from the egg as a 1/8-inch froglet. Full-grown and stretched out, it will fit on a postage stamp.
Where Do Poison Dart Tadpoles Live?
We might expect poison dart tadpoles to live in ponds. Some do.
But most dart frog mothers lay their eggs on the ground. How do
the tadpoles that hatch from these eggs find their way to water?
Frog mothers (or sometimes fathers) help tadpoles out of the jelly that surrounds the eggs. The tadpoles swim one at a time onto the parent frog's back, where they stick to the mucus on its skin. Then the parent carries the tadpole high into a tree to a pool of rainwater in a hollow or a bromeliad.
A bromeliad is a rainforest plant that grows on tree branches. Bromeliad's collect tiny pools of rainwater in the little pockets (called axils) where their leaves attach to their main stems.
Dart frog parents deposit their freshly hatched offspring into these tiny pools--only one tadpole per pool because tadpoles will eat other tadpoles. The tadpoles thrive on algae and mosquito larvae. In some species, mother frogs return every other day to lay an unfertilized egg in each nursery pool, providing more food for the tadpole. In other species, a father frog tricks another female frog into laying eggs, which he carries to the tadpoles.
Mutualism. The relationship between
poison dart frogs and bromeliads is a mutualism--a symbiosis that
benefits both organisms. The bromeliad provides the frog with
a safe nursery for its offspring. In turn, the frog supplies the
bromeliad with tadpole feces and decaying eggs, which make a rich
fertilizer.
How Do Poison Dart Frogs Climb Trees?
Their toes have tiny suction cups that cling to slippery leaves
and branches.
Why Are Dart Frogs Cool and Slimy? In
addition to toxin glands, dart frog skin is full of glands that
secrete a sticky or slimy mucus. This mucus helps keep them moist
and allows their skin to absorb water and air. Soggy leaf litter,
wet soil, and humid air also help keep their skin moist.
Like all frogs, dart frogs are "poikilothermic"--cold-blooded. Because they do not regulate their body temperature internally, they must rely on their habitat to keep them warm. Their rainforest homes are always about 80 degrees F, an ideal frog temperature. They also enjoy the dim light on the forest floor, where they are shaded by the thick tree canopy.
Species and Range. Dart frogs are classified
in the family Dendrobateidae. There are 170 known species in three
genuses, Dendrobates, Phyllobates, and Epipedobates. Some of these
species include auratus (green and black dart frog), azureus (blue
dart frog), histrionicus (harlequin), leucomelas (bumblebee),
pumilio (strawberry), Epipedobates tricolor (dyeing), Phyllobates
bicolor, and Phyllobates terribilis (golden). All are New World
species, ranging from Costa Rica to southern Brazil.
A few species are widely distributed, but most are limited to a small range. The species Dendrobates arborus--which lives its entire life in a tree--inhabits only a single mountain ridge in Panama. Among other species, the colors and patterns of individual frogs varies from one valley to the next or across a river.
Are Dart Frogs Endangered? Currently,
no dart frog species is in immediate danger of extinction. Like
all frogs, however, they are threatened by habitat depletion and
the pet trade. Because each species inhabits only a small region,
they are particularly vulnerable to loss of habitat. The dart
frog trade is regulated by CITES (the Convention on International
Trade in Endangered Species of Wild Fauna).
A GIFT FROM FROGS. A new drug, the painkiller ABT-594, has been synthesized from the toxin produced by Epipedrobates tricolor. Extracts from the frog were found to be 200 times more effective than morphine. Research has shown that ABT-594 does not hinder respiration, diminish bowel movement, or cause addiction.
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