Defence colony in eusocial insect is a costly but vital characteristic, whose evolution is modified by kin-selection forces resulting in self-sacrificing behaviour. Social aphids which cause gall reveal an amazing altruism as there are sterile soldiers which take care of defense, cleaning and even repair gall. Natural enemies still occur, but galls have nutritive, protective, and microclimatic perquisites as they are constituted by the secretion of insects and by such plant hormones as auxin and cytokinin. There is division of labour, the younger soldiers take the task of clearing waste and the older soldier's man vulnerable openings. Soldiers in certain species give themselves up by spilling body fluids in order to plug the breakages in the gall. These behaviours point to the adaptation value of gall induction and extreme altruism.