Avoiding ant detection in Siagona europaea Dejean 1826 (Coleoptera Carabidae): An evolutionary step towards true myrmecophily

Siagona europaea Dejean 1826, a carabid beetle living in clay soils of Mediterranean open lands, has been found to be an exclusive ant predator. Some morphological variations in body form are evidently adaptations to the habitat, favouring in the meantime the myrmecophagous life style. After capturing an ant, the beetle waves the prey held in its mandibles all around its dorsal forebody by arching its head and pronotum; the ants apparently spray a secretion over the beetle while being waved. The cuticular profle of beetles without contact with ants, beetles after capture and consumption of ants and of two ant species, Tapinoma nigerrimum and Messor capitatus, was recorded. Gas chromatography analyses revealed that more component are present on the carabid cuticle after predation and that they correspond to those of the tested ants. We suggest that this may be an intermediate evolutionary stage towards a true myrmecophilous life style as present in other tropical carabids. Moreover behavioural tests proved the diet (ants) which the beetle was fed triggers different reactions in ants of the same, or of a different, species.