In the dense, buzzing rainforests of Central and South America, an extraordinary story of mutual survival is unfolding in the canopies. Meet the Azteca ants and their Cecropia tree hosts—partners in one of nature’s most fascinating composting systems.
A partnership built over millenia
The Azteca-Cecropia relationship is a relationship that has developed over millions of years. The tree provides the ants with both a safe home in their hollow stems and a nutritious snack in the form of glycogen-rich food bodies.
In return, the ants fiercely protect the tree from both herbivorous invaders and encroaching vines. But, according to a new thesis by Veronica Barrajon Santos, the partnership doesn’t stop at defence. The ants also bring an ununexpected skill to the table: composting.
Composting in the canopy
Scientists already knew that Azteca ants can repair damage to trees with dark coloured patches. In fact, when holes were drilled in one tree, ants appeared and had completely replaired the tree within 24 hours.
These patches are built from materials like plant parenchyma (a tissue scraped from the tree’s interior), insect carcasses, moss, ants waste and even dead ants.
Far from being a waste dump, these patches appear to be perfectly engineered eco systems. When a new ant colony is founded, the queen brings microbes from her mother colony to innoculate the initial patch. As the colony grows, workers diversify the compost ingredients, adding moss, feces even dead ants, and the gungal diversity in these patches increases.
The waste in these patches is broken down by a mixture of funghi and bacteria, with the thriving microbial community supported by the ants able to decompose tough materials like cellulose and chitin.
Why Do Ants Compost?
The benefits of composting extend beyond nutrient cycling. The patches likely serve multiple purposes:
- Nutrient Reservoir: The decomposed material may nourish the ants and their larvae.
- Nest Hygiene: By breaking down waste, the ants prevent harmful pathogens from taking hold.
- Tree Support: The nutrients released from composting might help the host tree grow stronger, indirectly benefiting the ants by ensuring their home stays robust.
Source
Veronica Barrajon Santos, “In the tree farm of Azteca ants: A step forward in understanding the biodiversity and dynamics of ant-made patches in the stem of Cecropia trees,” Doctoral Thesis, 2024.