Tailless Caecilians: Caeciliidae

Physical characteristics: Mexican caecilians are 12 to 20 inches (30 to 50 centimeters) long and have a thick body. They are dark gray with paler markings on the belly, jaw, and tentacles. The grooves between the rings are darker than the main body color.

Geographic range: Mexican caecilians live in an area that extends from the lowlands and mountains of central Mexico south to northern Panama.

Habitat: Mexican caecilians live in moist soil that breaks up easily and in leaf litter.

Diet: Mexican caecilians are sit-and-wait predators. They eat invertebrates and vertebrates (VER-teh-brehts), or animals with a backbone, that live or travel in soil or leaf litter, including earthworms, Mexican caecilians are valuable to humans. They turn soil as they make their burrows, and they eat insects. (Illustration by Brian Cressman. Reproduced by permission.) termites, insects such as crickets that have shed their outer layer, and even small lizards and baby mice.

Behavior and reproduction: Mexican caecilians spend most of their time in burrows in loose, moist soil. They often come out at dusk in a light rain to look for food on the surface. These caecilians make their own burrows in many kinds of soil rather than using the burrows of other animals. Mexican caecilians move with an accordion-like motion and with side-to-side, wavy movements.

Mexican caecilians give birth to fully developed young. They are ready to reproduce when they are two to three years old. The male places the rear part of his cloaca into the cloaca of the female and transfers sperm directly to her reproductive tract. The cloaca (kloh-AY-kuh) is the chamber in some animals that holds waste from the kidneys and intestines, holds eggs or sperm about to be released to the outside, holds sperm entering a female's body, and is the passage through which young are born. Fertilization (FUR-teh-lih-ZAY-shun), or the joining of egg and sperm to start development, takes place inside the female.

Male Mexican caecilians make sperm eleven months of the year, but all females give birth at about the same time, in May and June when the rainy season begins. The young take eleven months to develop. Inside the female the developing young use up the yolk supply of their eggs about three months into the development period. The mother then releases a nutrient liquid from glands lining her egg ducts. The developing young move around in the egg ducts, eating the liquid. They have special teeth that they use to stimulate release of the nutrient liquid and to help take it into their mouths. These teeth are shed at birth, and the adult teeth, which are very different from those of the young inside the mother, grow out within a few days. The developing young have gills that have three branches, and each of the three branches has many more branches. The developing young use the gills and their skin to breathe while in the egg ducts. Gills are organs for obtaining oxygen from water.

Female Mexican caecilians give birth to three to sixteen young, which are 4 to 6 inches (10 to 15 centimeters) long at birth. These young are quite large considering the mother is only 12 to 18 inches (30 to 45 centimeters) long.

Mexican caecilians and people: Mexican caecilians are valuable to humans. They turn soil as they make their burrows, and they eat insects, such as termites, that can be harmful to people or their property.

Conservation status: Mexican caecilians are not considered threatened or endangered. Their numbers are high in some areas, but their habitat is being changed as trees are cut down to make way for farming. Mexican caecilians seem to adapt to some kinds of farm use. For example, there are large numbers of tailless caecilians on coffee farms, where the coffee hulls are thrown in piles to decay, thus forming the moist organic soil that is best for Mexican caecilians and their earthworm prey. ∎