Old soldiers never die ....

There is something truly intriguing about soldiers, individuals that specialize in the defense of the society they are part of. Small societies do not have specialized soldiers, because their enemies are invariably stronger, so keeping a low profile after abandoning camp is likely to be a survival strategy that is superior to fighting. Standing armies tend to arise when states become large and stratified, so that cities and territories are vast and precious enough to justify the expenses incurred. This logic appears to apply also in the advanced insect societies, in which most individuals are sterile workers that have lost the ability to reproduce. Ants are more likely to have a specialized soldier caste when they have large nests in the middle of defendable territories [1]. This so-called central-place foraging closely resembles the classic human city states, which originated as walled fortresses surrounded by their hinterlands [2].The same logic seems to explain why advanced social wasps and bees have only normal workers and no specialized soldier-morphs. Their workers are powerful defenders by default as they have both wings and stings and they operate in overlapping three-dimensional territories where competitors may dilute food intake but rarely eliminate neighboring colonies. The very first bee species that has a specialized soldier caste has just been discovered [3], an exception that proves the rule because it has an unusually large robber-bee enemy that can exterminate entire colonies. Thus, the costs and benefits of having a standing army seem straightforward, but the set of mechanisms by which individuals commit to a soldier career is poorly understood. Ant soldier caste differentiation is molded by natural selection at the colony level, but realized by individual development pathways that have rarely been studied in detail. A recent article by Rajakumar et al. [4] sheds intriguing light on the molecular mechanisms of caste development, and on the evoluti