Green iguana: why a hatchling eats an adult's droppings, according to a study
Published by Planète Pets · managing editor: Clément Lacaille · how our guides are written
An adult green iguana is a strict herbivore, able to draw energy from cellulose-rich leaves thanks to a fermentation chamber housed in its large intestine. But a hatchling comes out of the egg without the bacteria needed for that work. How does it acquire them? A study by Troyer, published in 1982 in the journal Science, uncovered a mechanism as simple as it is unexpected (see the study, doi 10.1126/science.216.4545.540). Find our other pointers in the reptile food section.
Contents · 6 sections
Hatchlings that grow poorly, for no obvious reason
The author observed that iguanas raised in captivity, isolated from hatching onward and fed correctly, grew markedly slower than wild hatchlings of the same age. Their gut failed to develop the complex bacterial population needed to ferment plant fibre, despite an apparently identical diet.
The fix: fresh droppings from an adult
By feeding captive hatchlings fresh fecal matter taken from an adult iguana, the study showed they rapidly acquired that complex flora and caught up with the growth of wild individuals. In the wild, young iguanas actually stay close to adults during their first weeks of life, a behaviour that seems to exist precisely to allow this contact and bacterial transfer, rather than for protection from predators.
Why cellulose doesn't digest itself
No vertebrate produces the enzymes able to break down plant cellulose. Herbivores that draw energy from it, iguanas included, depend entirely on symbiotic bacteria housed in an enlarged section of their digestive tract. Without them, the animal can eat as much greenery as you like: it will only digest a fraction of it.
What the study does not show
It dates from 1982, covers a small number of animals, and says nothing about the best way to inoculate a young iguana today without risking passing on the donor adult's intestinal parasites at the same time — a real risk, never to be taken lightly. Later work by the same author, in 1984, also showed that digestive capacity develops with age independently of this single bacterial acquisition: the real picture is more gradual than a simple switch.
What this changes in practice
A breeder or owner should not try to replicate this transfer themselves: the parasite risk outweighs the expected benefit. What the study does confirm is the value of regular veterinary check-ups for a young iguana and of a varied plant-based diet from the start, covered in our guide on feeding a green iguana. Find the full species profile on our green iguana page.
Frequently asked questions
Should you feed a baby iguana an adult's droppings?
No, never on your own initiative: the risk of passing on intestinal parasites is real and documented, far outweighing the benefit observed in this old study run under controlled conditions.
Does an incubator-hatched iguana still digest greens?
Yes, its digestive flora settles in gradually through contact with its environment and diet; growth may simply be a little slower at first than in a hatchling that stayed with adults. Find all our guides on the reptile hub.
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This guide is part of Planète Pets’s Reptiles universe. Our advice is general in nature: for any health concern, your veterinarian remains the only reference.