As its common name implies, the 2mm long Yellow ants’-nest beetle, Claviger testaceus, lives in the underground nests of the Yellow meadow ant, Lasius flavus, found in rough grassland.
This remarkable beetle has evolved into being a highly specialised parasite. Living entirely in a dark underground nest, it no longer needs eyes and so, over time, it has become blind (the optic nerves and visual centres in the brain have been lost). Because it remains in the nest the beetles have become wingless and the host ants carry them to new locations, and changes in the shape and structure of the wing cases provide increased resistance to the pressure caused by ants catching them with mandibles while moving them from place to place. Being handled and transported within the colony, the beetles’ antennae have become compacted to restrict damage.
The feeding behaviour of these beetles is also fascinating. Their mouthparts and associated muscles have become reduced, and they are unable to feed themselves. The beetles obtain nourishment, however, by inducing worker ants to disgorge food material meant for ant larvae. This is achieved by them producing a regurgitation chemical from glands inside their head (the brain has now shifted into the neck region to accommodate these glands!) – the chemical is then released onto short hairs by its mouth and is licked up by the ants. With such close proximity to the mouth of its host, the hairs, acting like capillaries, draw a drop of liquid food from the ant’s mouth directly into that of the beetle.
