Playing with the Dead: The Corpses of Dominant Territorials Inhibit the Activity of Subordinate Ants (Hymenoptera: Formicidae)

Necrophobia is a widespread phenomenon in animals. Contact with a dead body may involve a potentially fatal threat, as corpses are often sources of infections. Ants recognize corpses based on specific chemical cues and dispose of them by taking them out from their activity zone, frequently piling them up in so-called ‘cemeteries’. Necrophoresis (active disposal of corpses by physical removal), besides reducing the risk of infection for the particular species performing it, can also elicit necrophobia in other species living nearby. Some field observations suggest that in certain ant species corpses can be used to limit the activity of neighbouring colonies of competing species. In our study, we experimentally tested the effects of carcasses of dominant territorial Formica polyctena on the activity of F. cinerea ant under field conditions. We used F. polyctena workers freshly killed at low temperature with a preserved cuticular hydrocarbon profile and, for comparison, corpses stripped of their natural chemical label (washed in n-hexane). Our results confirmed the inhibitory effect of corpses, as the activity of workers correlated negatively with the number of corpses. On average the washed corpses reduced the ant activity by 9%, whereas the corpses with the preserved CHCs signature by 30%. Moreover, in some cases, the presence of washed corpses even increased the activity that did not happen in the other corpse type. Therefore, ant carcasses could be used as signals in interspecific competitive relationships. Whether, by whom and how common is their use should be the subject of further studies.