Caecilian Facts

Caecilian Profile

Caecilians are highly specialised, legless, long-bodied vertebrates with a variety of species found in humid, tropical regions of Central and South America, equatorial Africa and Southeast Asia.

Although their appearance is often likened to that of earthworms or snakes, caecilians are in fact amphibians, and are therefore more closely related to frogs and salamanders.

They are predominantly fossorial (adapted to burrow underground), and terrestrial, although there are aquatic and semiaquatic species.

Due to the fact that they live mainly underground, and are also present in harder-to-reach locations, these creatures are relatively poorly known and are rarely seen by humans.

Caecilians Facts

Caecilian Facts Overview

Habitat: Humid, tropical conditions. Loose soil, leaf litter, shallow running waters
Location: Central and South America, Africa, Asia
Lifespan: 4-5 years in the wild. Up to 13 years in captivity
Size: Varies by species. From 3.5 inches up to 5 feet in length
Weight: Up to 1kg, depending on species
Color: Varied. Grey to brown to purple or even blue
Diet: Carnivore: earthworms, insects, invertebrates
Predators: Burrowing snakes, fish, chickens, birds of prey, pigs
No. of Species: 219
Conservation Status: Mostly classed as ‘data deficient’. 6 species listed as ‘threatened’

There are 219 species of caecilian in 33 genera and 10 families, and while they are varied, they do have common traits as well.

All caecilians are virtually blind; they have very small eyes and mostly can only distinguish between light and dark. Since they spend almost all their time burrowing underground, they have little use for eyes, and have evolved as such.

Indeed, some species have skin completely covering their eyes, giving them a slightly gruesome appearance. Caecilians have very smooth, shiny skin – making them hard to catch and hold onto. Their skin exhibits a variety of colours – they can be grey, black, brown, yellow or even bright blue.

Some species are two-toned with purple colours on top and pink underneath. Some may even have stripes like that of a coral snake.

Their size varies quite dramatically depending on the species: the largest known caecilian is the Caecilian Thompsoni, which can grow to lengths of up to 60 inches; while the smallest is the Idiocranium Russell, a mere 3.5 inches in length. The larger species can weigh up to a kilogram.

As with salamanders, caecilians reproduce in different ways depending on the species: some lay eggs, while others give birth to live young. Aquatic species lay eggs in water, and in fact some terrestrial special produce aquatic larvae.

When these larvae hatch they have gills and a tail that help them move in the water to catch plankton. Gradually the gills are replaced with lungs, skin becomes thicker and the fully-developed adult moves onto dry land and burrows underground.

Other species lay eggs on land in moist soil, which hatch and remain with the mother for 4-6 weeks. With those species that give birth to live young, the infant caecilians are fully developed before they are born.

Caecilians are not dangerous to humans, although some species have evolved to release a toxin that can damage red blood cells in some animals. It is believed that this evolutionary trait developed to repel predators.

Interesting Caecilian Facts

1. Caecilians are not-well documented or studied

In fact, scientists have joked that the best-known fact about caecilians is that very little is known about them!

There is a lot that can still be discovered about this elusive collection of creatures, and scientists are still finding out about their lifestyles and habits. Much is yet to be learned about their interaction and communication, reproductive processes and lifespan. 1


2. Caecilians are powerful diggers

Despite the fact that they have no arms or legs, caecilians are able to burrow quickly and powerfully into dirt and soil using their robust skull and strong muscles that run the length of their bodies.

In experiments with similar sized caecilians, burrowing boas and mud snakes, the caecilians were observed to push at least two times more powerfully than their counterparts

3. Caecilians swallow their food whole

They only use their razor-sharp teeth for catching their prey, not for chewing it. instead, they will swallow their meal completely whole, like a snake. 2

4. Some caecilian species have developed an unusual way to feed their young

As amphibians, caecilians do not provide milk for their young like mammals do, nor do they catch food and return it to the nest, like birds.

However, caecilians of the Kenyan species Boulengerula taitana will allow their newly hatched young to scrape off and eat a layer of their skin.

The young caecilians are born with a special set of hooked teeth to allow them to remove this layer or skin without harming their mother in the process. 3

5. Caecilians are the only amphibians to have tentacles

These chemically-sensitive tentacles are located between the nostrils and the eyes and are used to help the animal navigate and find food.

Caecilians rely heavily on this chemosensory and tactile device due to their very limited or complete lack of vision. 4

6. The name ‘caecilian’ means ‘blind’

A slightly unusual ‘common name’, the word caecilian comes from the Latin word caecus, meaning ‘blind’ or ‘hidden’.

This is apt since the animals spend almost all their time hidden underground, and are virtually sightless. 5

Mexican Burrowing Caecilian

7. Caecilians are the first vertebrates to use their entire body as a hydrostatic system for movement

Their strong muscles and connective tissues enable them to dig, burrow and propel themselves along in the same type of movement seen in a piston or hydrostatic machine.

They are the first of their kind to use this kind of motion for locomotive purposes. Their very hard, pointed skulls are adapted to withstand the pressure from this powerful movement.

8. Even the aquatic forms of the species have lungs, not gills

All but one species of caecilians have lungs; like snakes, often one lung is significantly larger due to their body shape.

Even aquatic caecilians must return to the water’s surface to breathe. They have the ability to hold their breath for a long time; sometimes up to 30 minutes.

Caecilians are also able to absorb oxygen through their skin, and will more commonly respire this way. Young caecilians of the aquatic variety are born with gills which are gradually lost during metamorphosis. 6

Penis Snake

9. Most species lack tails

Although their long bodies may resemble a tail, the fact is that most species of caecilians do not have tails, or have a very small tail in relation to their body size. 7

10. Caecilians are threatened by habitat loss

As with many creatures on this earth, human activity is negatively impacting the lives of caecilians through the destruction and degradation of their habitat. Caecilians are also sometimes mistaken for snakes and killed.

There is one species of caecilians that are classed as endangered, while six species are classed as threatened. 8

Caecilian Fact-File Summary

Scientific Classification

Kingdom: Animalia
Phylum: Chordata
Class: Amphibia
Subclass: Lissamphibia
Order: Gymnophiona

Fact Sources & References

  1. Caecilians”, Science Direct.
  2. Mark Wilkinson “Caecilians”, CellPress.
  3. Caecilian”, San Diego Zoo Wildlife Alliance.
  4. Caecilians”, National Geographic.
  5. Aquatic Caecilian”, Smithsonian’s National Zoo & Conservation Biology Insitute.
  6. Caecilians: The other amphibian”, Science News Explores.
  7. Darren Naish (2013), “Because caecilians are important”, Scientific American.
  8. (2008), “Surreal caecilians part I: tentacles and protrusible eyes”, Science Blogs.