There is an interesting taster article (and ensuing discussion) on a new caste of soldier bees in a stingless bee of South America – the Jatai bee (Tetragonisca angustula).
Soldier bees guard their nest against attack by robbers
The study, published in the journal Proceedings of the National Academy of Sciences, found that Jatai soldiers are 30% heavier than their forager nestmates, have larger legs and relatively smaller heads.
Whats interesting is that this is the first known incidence of a soldier caste in bees – ants and other super-organism species have specialist solder castes but it had yet to be seen in bees.
Evolution is a wonderful (in the true sense of the word) phenomenon.
In the honey bee (in our hives – Apis melifera), the role of hive protection is undertaken by the worker bees who will sting intruders as a form of defense, and alarmed bees will release a pheromone that stimulates an attack response in other bees. Some honey bees species also use a ‘mob’ tactic where they crowd around an intruder (particularly wasps) in a ball. The ensuing heat and, possibly, carbon dioxide kill the intruder. They also use this ‘ball of bees’ tactic to starve/kill a queen to be superseded.
Further Links (based on Wikipedia):
C. H. Thawley. “Heat tolerance as a weapon”.
Michio Sugahara & Fumio Sakamoto (2009). “Heat and carbon dioxide generated by honeybees jointly act to kill hornets”. Naturwissenschaften 96 (9): 1133–6.
Victora Gill (July 3, 2009). “Honeybee mobs overpower hornets”. BBC News.