Cephalotes varians turtle ants. To enter her nest in a mangrove twig, a foraging worker must pass the door-guarding soldier whose head is roughly the same size and shape as the entrance. These ants don't build the nests themselves; rather, they inhabit burrows made by beetle larvae. Florida Keys, USA

Cephalotes varians turtle ant worker emerging from the nest. Florida Keys, USA

Podomyrma adelaidae tends to a Lycaenid caterpillar. These caterpillars secrete substances that the ants find attractive, and the ants in turn provide protection from parasites. Poochera, South Australia