Young protectors: Interspecific nest defense in the litlle fire ant Wasmannia auropunctata

In many social insects, division of labor is due to differences in age. In the little fire ant Wasmannia auropuctata, it has been recently found that the difference of age is identified by color, where lighter color ants perform nursing tasks while darker color ants perform foraging tasks. It has also been demonstrated that older workers perform nursing tasks when these are absent. In this study we evaluated age at which workers perform defense. We expected that as in honey bees, W. auropunctata nest defense should be carried out by older workers. We introduced a foreign ant and observed which ants (nurses or foragers) carried out nest defense. Our results show that defense is carried out mainly by nurses. This may be due to the fact that foragers are more valuable to the colony because they can also perform nursing tasks, while nurses only perform nursing task. Therefore selection may favor survival of foragers since these can ensure nest survival by bringing food as well as taking care of brood. Young individuals performing nest defense is atypical of social insects, making this study an important contribution to our understanding of social insect behavior and evolution.