Honeybees of the same hive are called nestmates. Sometimes, bees try to steal nectar from other nests. This is when the problem arises. The bee which stands guard at the entrance sniffs with its antennae to see if the bee that has arrived there belongs to the hive or not. If it is found to be an intruder, the guard bee stings it, thereby denying it entry into the nest. In the process of protecting the colony, the guard sacrifices its life.
Because sometimes honey bees steal nectar (the main ingredient for making honey) from other nests, some bees, called guard bees, stand at the door and sniff the bees that land there with their antennae. If the newly landed bee smells like she belongs in the nest, the guard lets her nestmate in. If not, the guard will bite and sting the intruder bee, preventing the intruder from entering the nest.
In experiments where scientists investigate how bees tell whether a bee is their nestmate or not, bees sometimes fail to recognise their nestmates and end up accidentally stinging their sisters! They also sometimes let bees into the hive that are not their nestmates.
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