Portrait of a mutualism: a swollen-thorn Acacia with the ants that protect it. The hundreds of thorns on a mature tree can house colonies of up to 20,000 ants. Chiriqui, Panama
Not all of the thorns on a swollen-thorn Acacia house the ants' larvae, but those that do are heavily guarded. Here, Pseudomyrmex spinicola patrol a nest entrance, ready to use their stings if the photographer approaches too close. Chiriqui, Panama.
Cutting open the surprisingly soft flesh of an Acacia thorn reveals larvae and pupae of the Pseudomyrmex spinicola acacia ant. Chiriqui, Panama.
