Well, half their mother. And it’s not really all that unusual either. Bees are the same way. The males (called drones) are hatched from unfertilized eggs laid by the queen. They have no stinger and can do no work for the hive. Literally their only purpose is to find another queen and mate with her, and then they die. They are basically nothing more than sperm with wings. So much so that, when it’s not mating season, the worker bees will often kick the males out of the hive to starve to death to conserve resources.