Honey bee stings have a barbed ratchet mechanism that pulls the stinger into the initial wound. This didn’t evolve as a suicide mechanism – honey bees can pull their stings out after stinging other insects.
It’s meant to drive the stinger in as deep as possible; it just happens that mammal skin is too fibrous to release the sting, so the abdomen is torn open when the bee tries to escape afterwards. Honey bees are the only species to suffer this fate, but the cost to the hive of losing some workers is worth it for an improved ability to repel honey thieves.
