Cephalotes varians, turtle ant soldier. The bizarre disc on the head is used as a living door to block the nest entrance. Florida Keys, USA

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