Why do bees sting and do they die?

A bee only stings under two conditions. To protect the colony or when frightened. When a bee stings, barbs in the lance of the sting cause it to firmly stick into the victim pulling out the venom sacs and glands when the bee is shaken off. The venom sac muscles continue to pump after these organs have been torn from the dying bee.

Only the female workers and the queen can sting, the queen having a smooth sting which she uses to kill other queens, while surviving herself.