If I were to mention an ant-fungus mutualism- that is, an ecological partnership between an ant and a fungus that benefits both- most biologically literate people might think of the famed leafcutter ants and the edible mycelia they cultivate.  But that is just one example.

Several other fungi have entered into productive relationships with ants, assisting especially in ant architecture.  Consider:

Lasius umbratus walking in the galleries of an underground carton nest (Illinois)

A larger view of the same nest. The intricate galleries are made from fungal mycelia growing through a matrix of ant-chewed wood pulp.

Here in North America, ants in the common subterranean species Lasius umbratus build extensive nests of chewed wood pulp. But wood pulp itself is flimsy, so the ants have recruited a fungus that grows through nest walls, strengthening the structures much like we humans use steel rebar to reinforce our concrete construction. The product is carton- a stiff, lightweight substance. Remarkably, no one has ever studied this relationship on our continent. All the research on Lasius and their fungi has focused on European populations.

Tropical ants also make carton with the help of fungi.  One recent study by Mayer & Volglmayr (2009) cultured several species from the arboreal runway galleries of Azteca brevis in Costa Rica.  Ant-plant ants in Allomerus and Aphomyrmex employ structural fungal symbionts as well, using them to bind plant trichomes into carton.

This Azteca carton shed in Guatemala houses mealybugs on the underside of a tree branch.

Where am I going with this post?

It’s that the more that we look in detail at life on earth, the more intricately interwoven we find it to be. There are microbes living on ant cuticles and bacteria digesting ant food.  The reason we know about the fungal symbioses is that someone went looking for them.  But as most ant species haven’t been screened for symbionts, the reality is we know hardly anything about the diversity that’s out there.  Just enough to know that many lifetimes’ of study await those who are curious about it.