Old and wise but not size: factors affecting threat response behaviour and nestmate recognition in Acromyrmex echinatior leaf-cutting ants

Detecting and responding to threats are of prime importance for social species which need to be able to distinguish nestmates from intruders to protect the resources of their colony. However, individuals may differ in their propensity to recognise threats due to factors, often intercorrelated, such as caste, age and experience, and the ability to separate these is important for understanding why behaviours are expressed. Here, we use leaf-cutting ants in a controlled behavioural assay to tease apart the factors which likely affect threat response behaviours in social insect workers. We show that foraging workers respond to threats more readily than do within-nest workers. The response of all workers was greater towards more foreign stimuli—nestmates rarely stimulated a response, whereas ants of a different genus stimulated a response in most cases. We show that age and experience act separately to increase an individual’s ability to perceive the threat. This suggests that where multiple, compounding factors affect the expression of certain behaviours it is important to realise that these factors can also have independent effects, particularly those which correlate with age. Separating the influence of correlating factors experimentally, as shown here, is particularly useful for understanding why individuals may differ in their behavioural profile.