To us, no doubt, one bee looks very much like another, and it is a mystery how the guards are able to recognise a strange bee. It is probable that the sense of smell has a great deal to do with this, for it is thought that all the bees of one hive smell alike, but differently from those of another hive, and that by this means the guards may detect a robber. A strange bee is never allowed to cross the threshold unless it is perhaps in the busy season, when the bees are “working overtime” as we might say, straining every nerve and muscle to gather in as much honey as they can before the summer goes and the flowers die. Then if a stranger comes to the hive, with her honey-sac full of the precious fluid, she may be allowed to pass in. Wasps often try to gain an entrance, as also do many other insects of one sort or another. If we watch the door for quite a short time in summer, it is pretty certain that we shall see several struggles. Sometimes it takes two or even three bees to expel the intruder. On one occasion I witnessed a fight which lasted well over half-an-hour between a robber bee and a guard bee. They rolled over and over on the board, this way and that, each trying to get the better of the other. At last they fell on to the ground below, but even then they did not stop the fight, and the struggle continued on the grass. Eventually the guard bee won the day, and by what appeared to be a final effort, she managed to pierce the abdomen of the robber bee with her sting. Instantly the robber bee was killed, and the brave little soldier bee returned to the hive in triumph. It is not easy for one bee to sting another, for the abdomen and thorax are so hard that it can only be done through one of the rings of the abdomen, where the skin is thin. CHAPTER XXIV WORKERS IN THE CITY