Bees have several options available to them when it comes to the matter of defense. Some species of bees have more types of defense than others, depending on relevant predation in the area. Bees have several areas where one might say they need, and indeed do have, natural defenses.
The first, and most obvious defense of most bees is the venomous stinger at the end of their abdomen. The stinger is heavily barbed in bees and only to a lesser extent in yellow jackets. The bee's stinger is believed to have evolved to wage inter-species war, and not to have stung mammals. This is the reason that a bee can sting other bees with no effect, but die as the barb lodges into thick, mammalian flesh, and rips out.
The bee is partner to several highly advanced evolutionary systems of defense. Many of these systems can be classified as chemical warfare. For instance, when a bee uses its sting in anger a pheromone is released that attracts other bees to the area, and informs them that the source of the sting is an enemy. In addition to its potentially lethal cocktail of venom, the bee is indeed a master of chemical warfare.
Another form of defense is, rightly enough, an excellent offense. The most aggressive, and offensive bee in the world, the African Honey bee, employs this strategy to great effect. The bees are highly territorial and quick to sting in defense of even a very generalized area surrounding their hive. The Africanized Honey bee may indeed posses the most effective bee defense system of all, considering the dozens of deaths that occur every year due to the massive amounts of venom injected by a swarm of these deadly insects. These bees are originally from Africa, but have spread throughout North and South America after an accidental release from a South American laboratory.
Bees also utilize camouflage in their plight to survive and thrive. Their yellow and black striping is believed to be harder to spot for birds and other potential predators. It may also serve to enable bees to recognize individuals within a swarm. Bees are surely one of the best defended flying insects. This is due to the obvious vulnerability while feeding on flowers and carcasses. The defense systems of bees have a direct correlation to the survival of humanity in its present condition. This is due to the necessity of having bees pollinate crops, crops that would otherwise bear no fruit and cause widespread famine.
An important defense for any bee exists at the cellular level. Bees must be resistant to several types of virus and human chemicals if they are to survive in close proximity to civilization. The recent phenomena of genetically engineered bees, have compromised several billions of bees' ability to adapt to their environment, and so are more prone to a mysterious ailment of bee colonies. This affliction is called Colony Collapse Disorder, and remains a conundrum to our understanding. Humans must take a greater responsibility in protecting this most precious resource.