Poison Frogs: Dendrobatidae - Physical Characteristics
Poison frogs are known for the very poisonous skin that many of them have. Actually, all frogs have poison glands, or small groups of cells, that ooze poison. In most species, the poison is very mild and, at most, only serves to make the frog taste bad. In some of the species in this family, however, the poison is far more potent and may even be deadly. The skin of the golden dart-poison frog, for instance, contains an especially dangerous poison, or toxin. Even the tiniest of droplets of this toxin in a predator's bloodstream can be fatal. Not all of the poison frog species are equally toxic, and some have no more poison than most other frogs in the world. Even within one species, different individuals may have different levels of toxin.
Scientists think that the especially toxic poison frogs may not actually make their toxins themselves, but instead get them by eating poisonous insects that, in turn, get their toxins by eating poisonous plants. The insects can eat the poisonous plants, and the frogs can eat the poisonous insects without having any health problems. When these especially toxic poison frogs are taken out of their natural habitat, placed in an aquarium, and fed non-poisonous food, the frogs eventually lose their high levels of toxins. The word toxicity (tox-ISS-ih-tee) means the level of toxins.
The toxic poison frogs are very colorful. These bright shades, called warning colors, caution predators against eating the frogs. The typical strawberry poison frog, for example, stands out with a bold red body and vivid blue legs. The Brazil nut poison frog has a black body with white to cream-colored spots and blotches on its back and red patches on its front and hind legs. People often describe these lovely little frogs as "jewels."
Those poison frogs that do not have especially toxic skin typically have much more drab colors, such as browns, tans, and olive greens. Often, these colors are in patterns that blend in with the frogs' surroundings. Rather than alerting predators to their presence, their colors camouflage them from predators. Stephen's rocket frog and the Trinidad poison frog are examples. Both are brown with darker brown stripes on the sides of the body and have dark banded legs.
In some species, like the strawberry poison frog, individuals may come in different colors. Those that live in one part of Panama are red and blue as described above, but those that live in other parts of the country may be green, yellow, or orange and may have a variety of patterns on their backs, including stripes or spots. Trinidad poison frogs are an example of a species with different-looking males and females. Both the males and the females have brown backs, but the males have gray throats with a black collar, while the females have the black collar but have bright yellow throats.
Perhaps the most unusual species in its appearance is the imitating poison frog. This small frog takes on a whole new look depending on its neighbors. If it lives near a Zimmermann's poison frog, the imitating frog looks like that species with its black-spotted yellow back, black-spotted blue legs, and blue belly. If it lives in the same area as the Amazon or Amazonian poison frog, which is an orange or yellow frog with long black stripes or spots, the imitating poison frog has that pattern. In addition, when the imitating frog shares a habitat with the red-headed poison frog, which is also known as the crowned poison frog, it has the half-orange or -red, half-black body of that species. The imitating frog is the only frog or amphibian known to copy, or mimic, the appearance of another amphibian. The imitating frog and all three of the species it mimics are highly toxic, but they are not close relatives of one another.
Regardless of the types of toxins in their skin or their colors, all poison frogs have a few things in common. They have powerful, although short, hind legs for leaping and, in some species, for climbing. They have thick pads of skin on the tops of their front and rear toes. The vast majority of them are also quite small. Most grow to 0.75 to 1.5 inches (1.9 to 3.8 centimeters) long from the tip of the snout to the end of the rump. The Brazilian poison frog and the blue-bellied poison frog are especially tiny. Female Brazilian poison frogs reach 0.68 to 0.8 inches (1.72 to 2.03 centimeters) long, and males are even smaller at 0.63 to 0.71 inches (1.6 to 1.8 centimeters) in length. Female blue-bellied poison frogs grow to 0.47 to 0.61 inches (1.19 to 1.55 centimeters), while the males reach just 0.47 to 0.59 inches (1.19 to 1.49 centimeters) in length. The Venezuelan skunk frog is one of the largest poison frogs. Females of this olive-green frog can grow to 2.5 inches (6.35 centimeters) long.