Class: Amphibia (Amphibians)
Body length: up to 2 inches (5 centimeters)
Weight: up to 2 ounces (56 grams)
Life span: 5 to 10 years
Incubation: 2 to 6 days to hatch; tadpoles metamorphose after 45 to 360 days, depending on species
Number of eggs laid: 10 to 100, depending on species
Size at hatch: 0.125 inches (3 millimeters)
Age of maturity: 12 to 14 months
Conservation status: five species are at critical risk, including golden mantella Mantella aurantiaca and green mantella Mantella viridis.
For many years, scientists believed that Madagascar’s mantellas and South America's poison frogs were closely related. But DNA studies have shown that they are only distant relatives with similar bright, warning colors!
Scientists have only recently discovered that some mantellas have skin toxins.
A group of mantellas is called an “army.”
Poisonous jewels of Madagascar
Tiny mantella frogs are among the most brightly colored and spectacular of all frogs. Most can be found in a variety of color combinations: inky black with brilliant splotches of orange, bronze, yellow, blue, or emerald green. These bright, eye-catching colors serve as a warning to predators that the little frogs are poisonous.
A toxic meal
Mantellas are found only on Madagascar, off the eastern coast of Africa. Many mantella species secrete toxins like those found in South America's poison frogs. They get alkaloid toxins from the prey that they eat, primarily ants, termites, and fruit flies. They then use these toxins for their own chemical defense. While not as deadly as the golden poison frog Phyllobates terribilis, mantellas secrete enough toxins to make a predator sick or, at the very least, they can make themselves taste quite bad!
Interestingly, human actions can affect how toxic a mantella might be. For example, mantellas living in areas that are left untouched by human activity have more alkaloid toxins in their bodies than those living in areas that have been polluted. Why is this? As humans move into mantella habitat or pollute it with contaminants, many of the frogs' prey items are killed off and there is less variety for the mantellas to eat. Fewer food choices means fewer alkaloids to be absorbed and, eventually, less toxic frogs.
Bright as day
All mantella frogs are poisonous, some more so than others, but they all still have the bright, beautiful colors that seem to shout, “I’m toxic!” This is known as protective mimicry, a very clever adaptation. By having the bright colors of the more toxic species, the frogs are avoided by predators. But the most glorious coloring in the world won’t protect you if you can’t be seen, and that is why all mantellas and poison frogs are diurnal, while most other frog species are nocturnal.
I like it cool and damp, thank you
Mantellas prefer relatively cool temperatures, and many are considered “upland” species because they are found at elevations above 1,600 feet (500 meters). Golden mantellas Mantella aurantiaca actually live at elevations above 2,900 feet (900 meters). Other species make their homes in lowland areas near Madagascar's coast. But no matter where the different species are found, they all need a damp environment: the more rain, the better!
Besides their bright colors, toxicity, and diurnal natures, mantellas also share some other remarkable similarities with their distant poison frog cousins. Both live almost entirely on land, although two mantella species spend a lot of time climbing trees. And, like poison frogs, mantellas are quite small, reaching no more than 2 inches (5 centimeters) in length. How can two animals that are not closely related end up being so similar? Both frog families evolved to fill similar niches, so they developed similar adaptations.
Rain brings new life
A female mantella waits until the first big rainstorm of the season and then deposits her eggs in damp leaf litter or in a short tunnel she has dug, depending on the species. The eggs hatch into tiny tadpoles a few days later. The little ones are washed by rainfall into small pools nearby, where they eat algae and grow. About 6 to 8 weeks later, the tadpoles have become wee froglets that measure about 0.4 inches (11 millimeters) in length, or about the size of a dime. The young frogs are a dull brown that keeps them well camouflaged in the leaf litter. During the next several months, they gradually change into the colors of the adults. They reach sexual maturity after a year and then live in small colonies with an average of two males for every one female. During the spring breeding season, males claim and protect territories, calling out to the females with a series of short, very rapid clicks. If another male mantella wanders into guarded territory, the owner wrestles with him and pushes him back out.
Most frogs have webbed feet to help them swim, but not mantellas! Because they spend their lives crawling around on land or in leaves instead of swimming, there is no need for webbed toes. They also have short legs designed more for climbing than for long hops. The arboreal mantella Mantella laevigata has swollen, sticky fingertips that help it hang on while moving around aboveground.
Indicators at risk
Like all amphibians, mantellas have skin that soaks up water. If something happens to change the water, amphibians are one of the first species to feel it. Much like frog species from all over the world, the health of mantellas can help scientists determine the health of Madagascar’s rain forests, air, and waterways. Because these frog populations are small, the slightest problem or mildest pollutant could be enough to completely wipe out a species.
Eleven mantella species are either at critical risk, endangered, or vulnerable. Threats to these delicate frogs include habitat loss, contaminants, introduced species, global climate change, and the pet trade. Some species, like the golden mantella, live only in tiny, limited areas, making them sensitive to overcollection by people wanting to have the colorful frogs as pets. The San Diego Zoo is involved in breeding two mantella species to learn more about them and to help preserve these jewels of the rain forest for future generations.