A Mexican caecilian (Dermophis mexicanus) at Saint Louis Zoo. Caecilians are legless, mostly blind amphibians.
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- From 3.5 inches to nearly 5 feet
Caecilians, pronounced seh-SILL-yens, may look like worms or snakes, but these long, lithe creatures belong to a group of legless amphibians. There are nearly 200 species of caecilians known to science, ranging from the 3.5-inch-long Idiocranium russell in Cameroon to the nearly 5-foot-long giant known as Caecilia thompsoni in Colombia.
Caecilians tend to have very small eyes, which are thought only to be able to detect differences between light and dark. In some species, the eyes are completely covered by skin—an adaptation suited to a life spent almost entirely underground. A pair of tiny, chemically-sensitive tentacles on the caecilians’ faces can detect food and possibly help the animals navigate.
While the amphibians possess no arms or legs, they are powerful diggers, using a strong skull and muscles that run the length of their body to drive through dirt and mud like a piston in a car engine.
Caecilians come in a variety of colors, from grays and blacks to brilliant blues. Some species are two-toned, with purple topsides and pink underbellies. Others boast dozens of vertical stripes, like a coral snake.
The skin of caecilians is smooth and slimy, and researchers note that catching one can be like trying to get a good grip on a bar of soap. Some species, like Siphonops paulensis of Central and South America, have glands in their skin that secrete toxins that can damage red blood cells in some animals. It’s thought that the toxic concoctions evolved to repel predators.
Habitat and behavior
Despite reaching gargantuan lengths, these animals are rarely seen by people. Most species spend a majority of their lives underground or plying the waters of shallow streams. Caecilians can be found in tropical and neotropical areas around the world, from Central and South America to Central Africa and Southeast Asia.
High up in the cloud forests of Ecuador, the giant caecilian known as Caecilia pachynema (pictured above) is only known to come to the surface at night and during torrential rainstorms.
Caecilians are not dangerous to humans, though the creatures do possess a mouth full of impressive, needle-like teeth. The rows of fangs help the animals capture prey, such as earthworms, which are then swallowed whole. They also eat insects and other invertebrates.
As amphibians, some caecilians lay their eggs in water or moist soil, similar to frog and salamander reproduction.
Interestingly, some caecilians have evolved a special way of caring for their young once they hatch. Rather than providing milk, as mammals do, or capturing prey and bringing it back to the nest, as birds do, female caecilians of the Kenyan species Boulengerula taitana allow their young to scrape off and eat a layer of their own skin.
A study published in Nature in 2006 found that brooding females in this species have skin that is up to twice as thick as females without young, and that the skin cells themselves may change in quality to offer the little ones more protein and fat. The young caecilians also come equipped with a special set of temporary teeth designed for scoring and lifting their mother’s epidermis off of her body without injuring her in the process.
There are also species that give birth to live young. And in some of these caecilians, scientists have found that the young will begin feeding on their mother before being born by gnawing away at the swollen lining of her oviduct. Scientists call this matriphagy.