Division of labour among workers with different life expectancy in the ant Myrmica scabrinodis

Workers present in the colony of social insects differ in age. The strategy of engaging younger workers in safer intranidal tasks, and older individuals in riskier tasks, for example, foraging, increases the average longevity of workers, and thus colony fitness. The transition to becoming a forager can be influenced by many environmental and social factors, but it has remained unclear whether the onset of foraging is also directly dependent on life expectancy. We tested this hypothesis with laboratory colonies of the ant Myrmica scabrinodis by creating groups of workers with reduced life expectancy. Ants were either anaesthetized with carbon dioxide or injured by removing their propodeal spines. Both treatments significantly shortened worker life expectancy in comparison to untreated control workers. Next, we showed that workers with an experimentally reduced life span became foragers earlier in life than control workers. This implies that ant workers adjust their threshold for engaging in risky foraging according to their life expectancy.