In a laboratory colony, a Cephalotes rohweri turtle ant soldier demonstrates how she uses her massive head to block the nest entrance. She is essentially a living door, and will not admit any ants other then her own nestmate. The second ant here is a Crematogaster acrobat ant, perhaps the turtle ants' biggest competitors for living space. Tucson, Arizona, USA

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