Some of the bees at the city gates are employed in quite a different manner; they do not fly afar in search of honey or pollen, but stand still, with heads pointing to the hive door. They are using their wings so vigorously that we cannot see them, just as the propeller of an aeroplane is invisible, because it is turning so quickly. These are the ventilating bees, whose duty it is to keep the hive cool on hot days. The quick fanning of their wings draws out the heated air from the hive, and if we were able to peep inside the door we should see other bees also engaged in the same occupation. These, too, stand with their heads towards the hive door, but instead of fanning out the hot air, as the outside bees do, they draw a stream of pure, cool air into the hive. By this simple and wonderful arrangement the bees are able to regulate the temperature to a nicety, for if it grows too warm, they have only to set more fanners to work, to expel the hot air. The temperature of the hive is a very important matter, for should it become too high the young ones would be suffocated, whilst if it dropped too low they would be starved to death. [Illustration: PLATE XIX Pollen gathers at Hive Door] The fanning is very hard work, and so, if we watch, we see that as a bee grows tired her place is taken by a fresh worker, and so the ventilating is constantly kept up. During the hot nights of summer, in the busiest time, the hive is thronged with workers who have come home from the fields to shelter from the dew and cold of the night. The city then becomes very crowded and hot, and a large army of bees must be kept at work ventilating. If, on such a night, we were to steal down to the hive with a lighted candle and place it a few inches from the door, the draught caused by the fanners would be quite strong enough to blow out the flame! CHAPTER XXIII THE GUARD BEES If we watch for a short time at the city gates, we shall very likely see two bees apparently fighting desperately. If we look closely we may see that one of the bees has hold of the other by the wing, and is dragging it away from the door. To and fro the fight rages, and the bee which is held struggles fiercely, but without avail, for the other has her in a firm grip. The captive bee is really a robber, which has been caught whilst trying to slip into the hive to steal honey. It may be that the robber is from another hive, or perhaps is a wild bee, for there are communities of bees which are really like pirates. They have their homes in some hollow tree, and live either by robbing other cities, or by waylaying workers on their return from the fields, and taking from them the honey which they have so laboriously gathered. The bees, therefore, have found it very necessary that there should be a guard at the gates of their cities, and there are always some soldier bees on sentry-go.