Peculiar Polydomy in Wood Ants (Hymenoptera: Formicidae): An Auxiliary Nest Seven Metres Underground

In this paper we show the unexpected fate of the odd Formica polyctena ‘colony’, spontaneously created at the bottom of a concrete post-nuclear bunker by workers falling into it en masse – with no way to leave – from their maternal nest located at the outlet of the bunker ventilation pipe (see Czechowski et al. 2016, Rutkowski et al. 2019). At the end of previous research, we inserted a wooden structure into the pipe to allow the ants trapped below to return to their maternal colony, which they did. Then it turned out that the ants, now able to move freely to and from the bunker, began to use the lower nest (in the form of an earthen mound) as an auxiliary nest for the colony, mainly as a winter nest (during the research period they inhabited it for two consecutive winters), and the bunker itself as a place for storing corpses and waste. We discussed these findings in the context of seasonal changes in temperature and relative humidity measured for the interior of the lower and upper nest mound and the air inside and outside the bunker. Our results highlight the extreme nesting flexibility shown by this species under very unusual environmental circumstances.