Siagona Europaea Dejean and Poecilus (Metapedius) pantanellii A. Fiori (Coleoptera: Carabidae): Two clay-soil dwelling species with different uses of the space

Siagona europaea and Poecilus pantanellii are two carabid beetles strictly bound to clay soils typical of the Italian Apennines. The first exhibits a very flat body whereas the other has more “normal” proportions, suggesting a very different use of space. We tested the use of space of both species using three sets of live pitfall traps put in place at different depths in the clay soil of a Mediterranean Hedysarum pasture. Poecilus pantanellii is a very early spring breeder and more than 90% of its individuals show epigean locomotory activity. Siagona europaea’s activity begins later, when the clay fissures become larger and deeper, and in the months of June and July about 80% of its population lives in the subterranean soil crevices. Morphometric measurements support these space use strategies: P. pantanellii has a wider antenna/eye angle and shorter antennae, indicating a possible visual component in prey recognition, as well as a thicker body and robust trochanters linked to “wedge pushing”; whereas S. europaea has longer antennae and a smaller antenna/eye angle suitable for olfactory-tactile prey recognition, and also has an extremely flat body and small trochanters. In the summer individuals climb up and down in the crevice system of clays searching for their specialised prey (worker ants exploring the space around their ant nests).