Worm-Like Amphibian Found to Produce Milk for Its Hatchlings; How Do Caecilians Nurse Their Young?

Lactation, the process of producing milk from the mammary glands to feed the young, is a unique characteristic of mammals. However, a handful of other animals, such as fish, birds, insects, and spiders, were found to secrete nutrient-rich liquid for their babies. This includes an egg-laying amphibian called caecilians, which produces a fatty substance that is functionally similar to mammalian milk.

What are Caecilians?

Caecilians refer to a group of limbless amphibians with small or sometimes non-existent eyes. They mostly thrive in soil or streambeds with a cryptic lifestyle that makes them the least familiar amphibians. They lay their eggs in water or moist soil, similar to the reproduction of frogs and salamanders.

These animals descended from the same family as frogs and salamanders. Hundreds of millions of years ago, their ancestors burrowed deep into the ground. As a result, they lost their legs, their bodies became long and segmented, and their eyes almost stopped working. The modern version of caecilian resembles a long shimmering earthwork with a head.

Although these creatures possess a mouth full of needle-like teeth, they are not dangerous to humans. The fangs help them capture prey, like earthworms, which are then swallowed whole. These animals also eat insects and other invertebrates.

An Unusual Diet

This group of around 200 species thrives in tropical regions. About 20 species are known to feed their babies with a milk-like substance. However, these species nurse their unborn offspring or those hatched inside their reproductive system. For the first time, however, scientists have identified an egg-laying amphibian that feeds its offspring hatched outside its body.

In the 2000s, scientists showed that in some caecilians, the babies hatched with teeth and fell on a nutrient-rich layer of their mother's skin every seven days. The details of this study were discussed in the paper "Milk provisioning in oviparous caecilian amphibian."

Naturalist Marta Antoniazzi led the research from the Butantan Institute. Antoniazzi noted that this behavior is a little strange, with hatchlings eating only once a week. That would not be sufficient for the offspring to develop as they do.

To better understand these bizarre feeding habits, Antoniazzi and her colleagues collected 16 nesting caecilians of the species Siphonops annalatus and their young from cacao plantations in the Atlantic Forest in Brazil. They filmed the animals and analyzed their behavior for over 200 hours.

The footage revealed that the young Siphonops annalatus not only munch on their mother's skin but also get their mother to release a liquid rich in fat and carbohydrates. This liquid is ejected from her cloaca, the combined rear opening for the digestive and reproductive systems. This practice is done by making clicking noises with high pitch. Afterward, the babies would stick their heads into the cloaca to feed.

This is the first time such communication and feeding practice has been seen in amphibians. According to experts, young caecilians may engage in begging behavior. The researchers believe their discovery could change the scientific understanding of reproductive evolution.