Caecilians are amphibians, like frogs and salamanders. They look like a mix between an earthworm and a snake. And they let their children tear off their skin and eat it.
Why you’ve never heard of caecilians
Unless you’ve taken a herpetology course or have a passion for amphibians, you’ve probably never heard of caecilians (pronounced suh-sil-yens). They’re not exactly a household name, even within their tropical range. Most caecilians keep a low profile by living underground. Caecilians are so under the radar that they’ve earned the title of “least known” order of terrestrial vertebrates.
Caecilians are so cryptic that 66% of caecilian species are classified by the IUCN as “data deficient,” meaning it is impossible to determine whether species are common or on the brink of extinction. Caecilians are difficult to study because most species must be dug out of their burrows in order to be observed. As a result, long term field studies on caecilians are few and far between.
What little we do know, we learned from projects such as that of Carlos Jared and his colleagues, who journeyed into the cacao plantations of Southern Bahia, Brazil, ten times from 2001 to 2017. The researchers dug in the soil, turned over fallen logs, and searched among decomposing plants for 703 person-hours and collected 71 specimens of the caecilian species Siphonops annulatus. That’s 10.5 hours spent searching by one person for each specimen collected. Compared with animals like insects, that can easily be collected in quantities of hundreds per person-hour depending on sampling method, it’s clear why caecilians are so under-studied.
What’s the story with the skin eating?
Like other amphibians, caecilians have glands in their skin that can secrete toxins and mucus. Uniquely in caecilians, though, skin can be used as a nutrient source for certain species’ young.
Caecilians have many different reproductive strategies. Some lay eggs, some give birth to live young; some care for their young, some don’t. Some mothers who take care of their hatchlings have a particularly eerie strategy for keeping their babies fed: the young litter of 5-16 caecilians swarms around the mother in a feeding frenzy, tearing off and eating the outer layer of her skin. They peel off the skin with specialized baby teeth, grabbing on to a piece of skin and rotating along their long axis until the skin rips off. Once mom has been peeled clean, the young wait until her outer layer of skin is ripe again. When the skin is ready to be removed, it turns a cloudy white color.
No one knows what happens to the mothers’ defensive skin secretions during feeding or whether caecilian young are resistant to the toxins. Either way, caecilian young survive and thrive thanks to the process of eating their mother’s skin, known as maternal dermatophagy.
In addition to eating skin, young caecilians have also been observed gathering at the mother’s cloaca (the vent at the posterior end of the body where waste is expelled) and ingesting some fluid. Newborn caecilians grow quickly, more than doubling their body mass in the first week after birth. In six weeks after birth, the young have attained the appearance of adults and leave their mother’s care. The mothers, on the other hand, never feed during the entire period of caring for their young, resulting in weight loss of up to a third of their body mass. After the young move on, mothers eat normally again and recover their lost weight.
More than meets the eye
The practice of skin-eating might sound brutal, but caecilians seem almost cuddly in some of their behaviors. There is no evidence of aggressive behavior or cannibalism between caecilians despite their voracious hunting and scavenging. Litterless caecilian mothers have adopted motherless litters and cared for them until maturity. Scientists even described these creatures as “gregarious and inoffensive” – which is about as close to “friendly and cute” as you can get in scientific literature.
Caecilians are bizarre, but somehow sweet. Like so much in nature, we can only marvel at the ingenious and unnerving ways these animals have learned to survive. And, as far as feeding our babies goes, be grateful we have our own way of doing things.
Jared, C., Mailho-Fontana, P.L., Jared, S.G.S., Kupfer, A., Delabie, J.H.C., Wilkinson, M., and Antoniazzi, M.M. 2019. Life history and reproduction of the neotropical caecilian Siphonops annulatus (Amphibia, Gymnophiona, Siphonopidae), with special emphasis on parental care. Acta Zoologica 100, pp. 292-302.