We have just said that there are sentinels at the entrance of every hive. They touch with their antennæ each individual that wishes to penetrate into the house. Hornets, the Death's-head Sphinx, slugs, &c., often try to introduce themselves into the hive. In that case, on the appeal of the watchful porters, all the bees combine their efforts to defend the entrance to their habitation. It would be impossible for them, in fact, to stop the ravages of their enemies when once entered into the interior. When a sphinx has succeeded in introducing itself into a hive, it sits down and drinks the honey in great bumpers, devouring all the provisions: and the unfortunate proprietors of the house are obliged to emigrate. To stop the entrance of moths which fly by night, the bees contract, and sometimes barricade, their door with a mixture of wax and propolis. When a slug or any other large animal has managed to introduce itself into the interior, they kill it and wrap it up in a shroud of propolis, as we have already related. However, they are quite helpless against certain microscopic parasites which sometimes attack them. The bee-louse, which has been described and drawn by Réaumur in one of his Memoirs,[95] and the parasite which was described in 1866 by M. Duchemin, the _Sugar Acarus_, which is found in the liquid honey of those hives which are attacked by the disease called the rot (_pourriture_), are the most serious enemies of the bee. The _Gallerias_ are also terrible enemies to them. Every hive thus attacked is ruined. These destructive insects attack also the wild bees, drive them from their nests, and destroy the wax of the cakes forming the comb. The _Galleria_ impudently makes his home in the houses of bees, wild as well as domesticated. [95] Tome v., planche 36. The habits of bees in their wild state, which make their nests in the trunks of trees and other cavities, do not differ from those of domesticated bees. Only the latter become tame with man, getting used to those who look after them, and becoming less aggressive towards strangers. Apiculture, or bee-keeping, is still at the present day an important business, although honey has lost a great deal of its utility since the introduction of sugar into Europe. Without entering into many details on apiculture, that is to say, on the attention it is necessary to pay to bees, we will mention the principal duties of the bee-keeper.