APPEARANCE
Poison frogs are jewels of nature. They are among Amazonia's most colorful, smallest and famous
animals. Yet, much remains to be learned about these charismatic creatures.
Grouped in the taxonomic family Dendrobatidae, most poison frogs are tiny, an inch (2.5 cm) or less in
length. The largest species are up to 2.5 inches (60 mm) long. The famous herpetologist William Duellman
reports that about 220 species are known, divided into 10 genera (Duellman 2005). Given the small size of
these creatures, many more undoubtedly remain to be discovered.
Among the species, every color of the rainbow is represented. The bright colors advertise the toxicity of
the animal. Primary colors—red, yellow and blue— are common. Contrast of colors likewise, such as
red and blue, black and yellow, serve to grab attention. So fearless are these animals, on account of their
poison, that they hop around regardless of apparent threats. This is an example of aposematic, or warning, coloration.
Many species have three to five longitudinal stripes from the snout to vent, while spotting of colors on
the hindquarters is also common. Some species have giraffe-like splotches, large spots covering the body.
Most species have smooth skin, although others have a granular texture more typical of toads. The skin of
the frog is permanently moist and exudes the poison. Much of the toxicity is derived from the diet of the
frogs in nature, mostly ants. Frogs raised in captivity gradually lose their toxicity.
Indeed, these frogs harbor among the most potent toxins of any animal, rivaling such fearsome poisons as
that of elapid snakes and cone shells. One beautiful bright yellow species from Colombia, Dendrobates
terribilis, is so poisonous that merely handling an individual can admit enough poison through the skin
to produce symptoms of poisoning.
According to Kricher (1992) around 300 poisons called alkaloids have
been isolated from amphibians, including over 100 toxins from skin frogs of the Dendrobatidae family
(especially Dendrobates and Phyllobates). The most deadly of these is batrachotoxin, a nerve
poison produced only by species of the genus Phyllobates. Batrachotoxin is ten times more potent than
tetrodotoxin from the puffer fish. For
example, the lethal dose of batrachotoxin for an average adult would be the equivalent of two grains of
ordinary table salt.
Note on nomenclature
Poison frogs are widely called poison arrow frogs or poison dart frogs, reflecting the widespread belief
that Indians use the frogs in the manufacture of poison that is spread on arrows or blowgun darts. However,
the practice seems quite restricted, with most arrow or dart poisons being a form of curare, which is
derived primarily from plant toxins. Kricher (1997) mentions that the Choco Indians of western Colombia use
compounds "extracted from the frogs' skins" but he does not mention usage by other tribes.
Therefore, the preferred name among some herpetologists is to call this group "poison frogs."
HABITAT AND DISTRIBUTION
Most species of poison frogs are diurnal. They are restricted
to regions of tropical rainforest, usually where temperatures remain above 20°C year-round. As a group,
they range from the forest floor to the canopy, and individual species tend to specialize in such
niches.
FEEDING AND DIET
Duellman (2005) gives detailed accounts of the diets of several poison frog species. Numerically, ants and
mites comprise the majority of prey, with ants alone making from a third to two-thirds of their food. Other
food items include springtails, flies, spiders, beetles and insect larvae. The diet is significant in the
physiology of these frogs because the potency of their skin toxins diminishes when in captivity they do not
have access to their wild diet. Researchers have shown that the precursors of batrachotoxins (one of the
classes of alkaloid poisons found in dendrobatid skins) are found in dietary components, ants in particular
(Kricher 1997).
BREEDING
Like most frogs, dendrobatids advertise territory and breeding status with vocalizations. The notes consist
of peeping sounds, with several peeps per second. The rate and pitch of the calls are distinctive between
species. A skilled listener can readily distinguish species based on their calls. An unskilled listener,
hearing the high frequency chirping during the day might mistake the call for a cricket or cicada.
Breeding takes place during the rainy season.
Poison frogs are remarkable for the degree of parental care shown to young. Most amphibians spawn in a pond
or puddle and leave the eggs and tadpoles to fend for themselves. Poison frogs typically lay just a handful
of eggs (primitive non-toxic species may lay 25 to 30). Details vary among species, but the general picture
is as follows.
Dendrobatids do not deposit eggs in water. In some species, the female deposits eggs on leaves among leaf
litter on the forest floor. In others, the female attaches her eggs above the waterline inside a bromeliad rosette or tree hole.
When the eggs hatch, the parent (male or female, depending on species) rests in the water while the tadpole
wriggle up onto its back. A type of glue, water-soluble mucopolysaccharides, helps attach the tadpole to
the back. The parent wanders off carrying its young (like a backpack baby carrier), to a suitable home,
another bromeliad tank, pond or slow-moving stream. The parent rests a while in the water, the glue
dissolves and the tadpoles swim off. Depending on the species, the parent may carry each tadpole to a
separate aquatic site, thus spreading the risk of having all her "eggs in one basket" (or tadpoles
in one puddle).
In several species of dendrobatids, the female returns every five days or so to the developing tadpole.
There she deposits an unfertilized egg in the treehole, below the waterline. This dud egg is then consumed
by the tadpole, thereby providing it nutrients that may be lacking in the treehole. The poor food supply of
this environment has led to predatory behavior among species of the Dendrobates genus. All other
members of the family eat algae or detritus in their watery homes. Among Dendrobates, the ability to
eat small aquatic invertebrates such as mosquito larvae would have been beneficial, to the point where
Dendrobates now prey on other tadpoles. Hence, as described above, the parents of some species
transport their tadpoles singly so they can develop in isolation, safe from their hungry siblings.
CONSERVATION
The conservation status of these frogs is not well known due to the practical difficulties of conducting
comprehensive field surveys.
They're not hunted (aside from rare use as arrow poison, see above),
although collecting may have an impact. However, since many species of these frogs readily breed in
captivity, pressure on wild populations from collecting is probably sporadic.
No species of poison frogs are listed by the IUCN, and none are known to have gone extinct. However, the trade in
many species is controlled (CITES II) and we can infer that destruction of their native habitat causes local
extinctions. Given the narrow geographical range of many species, and quite specific habitat requirements,
widespread deforestation would certainly threaten particular species.
REFERENCES
Duellman W. E. (2005) Cusco Amazónico: The Lives of Amphibians and Reptiles in an Amazonian Rainforest. Comstock Publishing, Cornell University Press, Ithaca, NY.
Kricher J. (1997) A Neotropical Companion. Princeton University Press.
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