Ringed Caecilian

The ringed caecilian is a member of the strangest and least familiar group of amphibians — the caecilians, legless burrowers that look like large earthworms and spend their lives out of sight in tropical soil. This South American species has recently made headlines for two extraordinary traits: mothers that feed their young their own skin, and the possible discovery of amphibian venom.

Overview

Siphonops annulatus is one of the most widespread and frequently encountered caecilians, found in moist soil across much of South America east of the Andes — in forest, but also in plantations, gardens, and pasture, wherever the ground is soft and damp enough to tunnel through and rich in earthworms and termites. Even so, it is almost never seen unless dug up, and in Brazil it is often mistaken for a snake and called cobra-cega, “blind snake.”

Built for the dark underground

Caecilians have discarded nearly everything associated with the amphibian body:

• No limbs or limb girdles — they move by driving the pointed, bony skull forward and pushing with waves of muscle, like an animated screw.
• Reduced eyes, often buried under skin or bone; vision is nearly useless underground.
• A unique chemosensory tentacle that can be extended from a pit between the eye and nostril to taste-smell the soil ahead.
• Ring-shaped grooves down the body that, with the compact head, complete the earthworm disguise.

Feeding the young with skin

The ringed caecilian’s parental care is remarkable. The female lays eggs on land and coils around them, and after the young hatch she develops a special thick, fatty outer skin layer that the hatchlings peel off and eat using purpose-built deciduous teeth. She regenerates the layer every few days, and this “dermatophagy” — skin-eating — is the young’s main food for their first weeks. It is a form of maternal provisioning found in only a handful of animals.

The venom question

Long assumed to be harmless, the ringed caecilian may in fact be the first amphibian shown to have oral venom glands. Researchers found small glands at the bases of its teeth, and later work reported they contain proteins related to those in reptile venoms and connect to tooth grooves. If a biting venom-delivery system is confirmed, it would be evolutionarily separate from — and much older than — that of snakes, and unlike the toxic skin secretions of poison frogs and some salamanders.

Status

The ringed caecilian is listed as Least Concern — it is common, tolerant of disturbed and agricultural land, and not currently threatened. Caecilians as a group are, however, badly understudied, and many localised species with tiny ranges are probably at risk from deforestation, soil degradation, and the amphibian diseases spreading worldwide, without anyone yet knowing.