Worm-like caecilian produces a kind of milk for its hatchlings

A worm-like creature secretes a nutritious milk from its rear end to feed its hatchlings, in the first known example of an amphibian feeding its young in this way.

The ringed caecilian (Siphonops annulatus) is a legless, egg-laying amphibian that can be found in dark, moist forest floors across South America. It reaches up to 45 centimetres in length, with white grooves encircling its deep blue, cylindrical body.

Ringed caecilians are born with spoon-shaped teeth. They use these to feed on their mother’s skin, which is rich in lipids and proteins.

“But this skin feeding only happens once a week,” says Carlos Jared at the Butantan Institute in São Paulo, Brazil. That isn’t enough food to sustain the rate at which the young develop, he says, with some growing 150 per cent larger within their first week of life.

To find out where their extra nutrition comes from, Jared and his colleagues recorded videos of 16 female ringed caecilians and their hatchlings.

The team observed the hatchlings wriggling around the end of their mother’s body several times a day, often nibbling and sticking their heads into a posterior orifice, known as a vent.

Closer inspection of the footage showed small drops of a milk-like substance often spilling onto the vent’s opening, which suggests that the young were actively feeding on it.

Analysis of the milk revealed that it contained lipids and carbohydrates. “These carbohydrates are very important,” says team member Pedro Mailho-Fontana, also at the Butantan Institute, as they give the hatchlings the energy they need to grow.

The team also found that touch and sound signals from the hatchlings stimulated milk production in glands within the mother’s oviduct, or fallopian tube.

Some caecilians that give birth to live young secrete nutritious fluids for the fetuses inside the mother’s body, says Mailho-Fontana, but this is the first time amphibians have been found to produce fluid to feed their young outside the body.

“Caecilians are a real surprise box,” says Jared. “They’re very secretive, living inside the subterranean world, which is different to the surface of the earth. They adapted in a world completely different to what we know and needed to invent several new behaviours to live.”