Phragmosis

Some species, such as Pternohyla fodiens and Corythomantis greeningi, have evolved a peculiarly casqued head adapted to protect the animal as it backs down a hole.

[2] The behaviour is displayed in numerous taxa such as Camponotus, Colobostruma, Crematogaster, Pheidole, Blepharidatta, Cephalotes pusillus, Carebara elmenteitae, Stenamma expolitum, in which the soldiers have unusually large, disc-shaped heads, which are used to block nest entrances against intruders.

[3] Recent studies of Corythomantis greeningi, a casque-headed tree frog from semi-arid areas, have provided substantial information regarding the water economy associated with co-ossification of the head.

[3] Due to the arid environments of most casque-headed anurans, it has been proposed that head co-ossification, together with phragmotic behaviour confer protection against water loss.

This type of skull morphology primarily acts to protect the animal against predators, and in doing so, leads to an indirect enhancement of water balance within the body.

[4] Astegopteryx soldiers effectively defend their subgall by plugging the ostiole nearly completely with their sclerotic, spiny heads, which are very likely to have evolved for that purpose.

[2] Phragmosis in ants has evolved independently in the diverse ant genera Camponotus Mayr (Hypercolobopsis), Colobopsis Mayr, Cephalotes Latreille,[6] Colobostruma Wheeler (C. leae), Crematogaster Lund (Colobocrema), Pheidole Westwood (P. colobopsis, P. lamia), but also in other genera, such as Blepharidatta Smith, (B. conops), Tetraponera Smith (T. phrag- motica) and Carebara Westwood.

[7] The shield-like armor which characterizes this behaviour enables plugging of nest entrances, without exposing eyes, antenna or mandibles to any potential intruders.