Seasonal changes in host ant aggressiveness towards social parasites of different types

Pécsy, Fanni and Lőrinczi, Gábor and Bán, Kata Anna and Lőrincz, Ádám and Ratkai, Bonita and Czechowski, Wojciech and Maák, István Elek (2026) Seasonal changes in host ant aggressiveness towards social parasites of different types. ANIMAL BEHAVIOUR. ISSN 0003-3472 (print); 1095-8282 (online) (In Press)

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Abstract

Social parasites are social insects that exploit the labour and resources of other social insects. In ants, several types of social parasites are known, including temporary parasites, in which host workers are present only during colony founding, and slavemaker ants, which continually supplement their workforce with host workers throughout the colony’s lifetime. Because defence against parasites is costly, host species are expected to modulate their responses according to parasite-imposed risks. In this study, we investigated the seasonal patterns of aggressiveness in a common host Formica fusca (silky ant), towards its temporary social parasite (Formica polyctena, European wood ant) and a slave-maker (Formica sanguinea, blood-red ant). Behavioural assays were conducted in spring, summer, and autumn using host workers collected from colonies located (1) near F. polyctena colonies, (2) near F. sanguinea colonies, and (3) in parasite-free (control) areas. Hosts from areas dominated by F. polyctena were more aggressive towards F. polyctena in spring and summer than in autumn, showed peak aggression towards F. sanguinea in summer, and were more aggressive towards F. sanguinea than F. polyctena in summer and autumn. Hosts from areas with F. sanguinea displayed the highest aggression towards both parasite species in spring and summer, with similar responses to both parasites across all seasons. Control colonies showed an intermediate pattern, combining elements of both responses. Seasonal variation in host aggressiveness appears to track differences in the timing and severity of threats imposed by the two parasites: colony founding by F. polyctena in spring and early summer, and slave raids by F. sanguinea in summer. Such temporal adjustment of defensive behaviour may help minimize the costs of defence against social parasites by increasing aggression only when the threat is greatest.

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