Marion Cordonnier

Neighbour–stranger response differences (NSRDs) are when individuals are either more aggressive (“Nasty Neighbour”) or less aggressive (“Dear Enemy” or “Dear Neighbour”) to direct neighbours than to other competitors perceived as “strangers” by the residents. Such effects are often reported in ants which, being fixed‐location central‐place foragers, may compete directly with their neighbours for resources or raid each other for brood. Overlayed onto this are potential spatial distance and relatedness effects on aggression, which are often not differentiated from NSRDs. The literature on NSRDs and distance effects in ants does not reveal a systematic pattern across all ants due to their diversity of life histories, requiring each species to be evaluated individually. Lasius niger is a common Eurasian ant species, which can form very dense populations of colonies and shows pronounced nestmate recognition, so may be expected to show NSRDs. Here, we take advantage of a semi‐regular colony array to examine the effect of spatial distance and relatedness on aggression and probe for NSRDs. Overt aggression does not vary with relatedness or spatial distance, and there is no evidence that direct neighbours represent a special case in terms of aggression. However, antennation and jerking decrease between less related and more spatially distant pairs, but are almost completely absent from allospecific interactions. We tentatively propose that antennation and jerking together represent a ‘negotiation’ phase, which may either precede or reduce the need for overt aggression. While a Nasty Neighbour effect might occur, a Dear Neighbour effect is unlikely in this species, and overall NSRDs do not play a large role in the ecology of this species. More broadly, this work highlights the importance of considering non‐overtly aggressive responses when studying NSRDs.