A bee sting is a sting from a bee (honey bee, bumblebee, sweat bee, etc.). The stings of most of these species can be quite painful, and are therefore keenly avoided by many people.

The stinger consists of three parts: a stylus and two barbed slides (or lancets), one on either side of the stylus. The bee does not push the stinger in but it is drawn in by the barbed slides. The slides move alternately up and down the stylus so when the barb of one slide has caught and retracts, it pulls the stylus and the other barbed slide into the wound. When the other barb has caught, it also retracts up the stylus pulling the sting further in. This process is repeated until the sting is fully in and even continues after the sting and its mechanism is detached from the bee's abdomen.

A honey bee that is away from the hive foraging for nectar or pollen will rarely sting, except when stepped on or roughly handled. Honey bees will actively seek out and sting when they perceive the hive to be threatened, often being alerted to this by the release of attack pheromones.

When a honey bee stings a person, it cannot pull the barbed stinger back out. It leaves behind not only the stinger, but also part of its abdomen and digestive tract, plus muscles and nerves. This massive abdominal rupture kills the honey bee. Honey bees are the only bees to die after stinging.

More Info: en.wikipedia.org