Different nest entrance architecture by Colobopsis and Temnothorax ants colonizing oak galls

Galls are neoformed structures induced on the tissues of a host plant by different organisms, mostly insects. Apart from the inducers, galls can also provide shelter to several different arthropods, referred to as secondary occupants. In certain types of galls, ants are among the prevalent secondary colonizers. This study focuses on oak galls induced by the cynipid wasp Andricus quercustozae and secondarily colonized by two ant species, Colobopsis truncata and Temnothorax italicus. We provide a first characterization of the architectural differences concerning the way they reduce the size of the exit holes excavated by the adult cynipds in order to transform them in their nest entrances. The nest entrance holes differed markedly between the two species in their size and positioning, as well as in the construction material. C. truncata built larger entrance holes with a more central position, apparently facilitating the defensive ability of the phragmotic soldiers, while the smaller nest entrance hole by T. italicus were located in a lateral position. On the other hand, only T. italicus mixed dead insect fragments in the construction material (including the defensive hastisetae of dermestid larvae), probably due to a more insectivorous diet compared to C. truncata.