Keep the nest clean: survival advantages of corpse removal in ants

Abstract

Sociality increases exposure to pathogens. Therefore, social insects have developed a wide range of behavioural defences, known as 'social immunity'. However, the benefits of these behaviours in terms of colony survival have been scarcely investigated. We tested the survival advantage of prophylaxis, i.e. corpse removal, in ants. Over 50 days, we compared the survival of ants in colonies that were free to remove corpses with those that were restricted in their corpse removal. From Day 8 onwards, the survival of adult workers was significantly higher in colonies that were allowed to remove corpses normally. Overall, larvae survived better than adults, but were slightly affected by the presence of corpses in the nest. When removal was restricted, ants removed as many corpses as they could and moved the remaining corpses away from brood, typically to the nest corners. These results show the importance of nest maintenance and prophylactic behaviour in social insects.

Keywords: Myrmica rubra; necrophoresis; social immunity; survival, ants.

Figure 1.

(a) Survival curves of workers (mean ± s.e.). (b) Survival curves of larvae (mean ± s.e.). Squares, FR colonies; circles, LR colonies.

Figure 2.

Boxplots represent the relative distance of corpses from the larvae patch. Above each pair of boxplots is a miniature of the nest (85 × 85 mm) on a given day after the introduction of corpses, where each small black dot represents one corpse (data from all colonies are pooled).