his thorax above her abdomen, straddling her. He then grasps her with all six legs, and everts the endophallus into her opened sting chamber. If the queen's sting chamber is not fully opened, mating is unsuccessful, so some males that mount the queen do not transfer semen. Once the endophallus has been everted, the drone is paralyzed, flipping backwards as he ejaculates. The process of ejaculation is explosive—semen is blasted through the queen's sting chamber and into the oviduct. The process is sometimes audible to the human ear, akin to a "popping" sound. The ejaculation is so powerful that it ruptures the endophallus, disconnecting the drone from the queen. The bulb of the endophallus is broken off inside of the queen during mating—so drones mate only once, and die shortly after. The leftover endophallus remaining in the queen's vagina is referred to as the "mating sign". The plug will not prevent the next drone from mating with the same queen, but may prevent semen from flowing out of the vagina. Drone congregation areas Mating between the drones and a virgin queen takes place away from the colony, in mid-air mating sites. These mating sites, called 'congregation areas', are specific locations, where drones wait for the arrival of virgin queens. A congregation area is typically above ground, and can have a diameter of . The boundaries of a congregation area are distinct; queens flying a few meters outside the boundaries are mostly ignored by the drones. Congregation areas are typically used year after year, with some spots showing little change over 12 years. Since drones are expelled from a colony during the winter, and new drones are raised each spring, inexperienced drones must find these congregation areas anew. This suggests some environmental cues define a congregation area, although the actual cues are unknown. Congregation areas are typically located above open ground, away from trees or hills, where flight is somewhat protected from the wind (calm winds may be helpful during mating flight). At the same time, many congregation areas do not show such characteristics, such as those located above water or the forest canopy. Some studies have suggested that magnetic orientation could play a role, since drones older than 6 days contain cells in the abdomen that are rich in magnetite. Congregation areas can be located by attaching a virgin queen (in a cage) to a balloon floating above ground. The