Honey bees are subject to predation on stored food or on the bees in the colony. Two distinct sorts of predators may attack colonies; other bees, which may rob food from the colony, or vertebrates, which may be after stored food, brood, or adult workers.
In my lab we have characterized the bees that defend against these threats. Guard bees keep other bees out. They stand at the nest entrance, antennate incoming bees, and attack bees that don't belong. Guards are younger than the typical forager, and often become foragers later in life. Soldiers fly up and attack vertebrate predators. Soldiers are the same age as foragers, but do not forage.
Current research on colony defense in my lab includes projects on the sensory modalities used by guards to distinguish nestmates from non nestmates and on the behavior of soldiers after they have stung.

Papers on this topic from my lab:

Moore, A.M., Breed, M.D., Moor, M.J. 1987. The guard honey bee; ontogeny and behavioral variability of workers performing a specialized task. Anim. Behav. 35:1159-1167.

Breed, M.D. 1988. The guard bee and honey bee defensive behavior. in Proceedings of the Africanized Honey Bee and Mite Conference, R.E. Page, G. Needham, M. Delfinado-Baker, eds. Ellis Horwood Publishing Co. pp. 105-109.

Breed, M.D., Rogers, K.B., Hunley, J.A., Moore, A.J. 1989. A correlation between guard behavior and defensive response in the honey bee. Anim. Behav. 37:515-516.

Breed, M. D., Robinson, G. E., Page, R. E. 1991. Division of labor during honey bee colony defense. Behav. Ecol. Sociobiol. 27:395-401.

Breed, M. D., Rogers, K. D. 1991. The behavioral genetics of colony defense in honey bees: Genetic variability for guarding behavior. Behav. Genet. 21:295-303.

Breed, M. D., Smith, T. A., and Torres, A. 1992. Guard honey bees: role in nestmate recognition and replacement. Annals Entomol. Soc. Am. 85:633-637.