§. VI. PROPOLIS, OR BEES' CEMENT.
"Propolis" is a Greek word which originally signified "the outskirts of a city," but was adopted by Latin writers on bees to denote the sticky substance with which these city-rearing insects protect their outskirts. It is "a resinous substance, very tenacious and semi-transparent," which is indispensable for the bees as a cement wherewith to fix their combs and fortify their hives against intruders.[33] The bees, in working the propolis, often soften it by blending it with a portion of wax; but they have to extract it in its natural state directly from the bark and buds of certain trees. The bark of the willow, the leaf-buds of the poplar and alder, and the unopened blossoms of the hollyhock are very usual sources of propolis. In the case of a new swarm, as bees must have this glue before they can begin to build their combs, they will resort to most unlikely places to obtain it. Sometimes they will enter a paint-shop and attack the varnish, and it is said they have been seen to obtain propolis from the pitch and rigging of a ship. These circumstances afford intelligible hints to the apiarian, who, if his bees have not easy access to firs, poplars, or willows, will provide some glutinous or resinous matter which may serve for a substitute. The extraction of propolis costs the bees very considerable labour, which they should be relieved of as much as possible in order to facilitate their great work of honey-gathering. Bees choose the warmer part of the day during which to gather propolis, as then it does not so rapidly stiffen. Frequently when they arrive at the hive it has become so hard that the other bees are scarcely able to gnaw it from their thighs.
[33] Egyptian bees, however, substitute wax, as stated on [page 50].
With propolis bees fasten down their hives, stop up crevices, to exclude moths and ants, and sometimes use it to narrow their doorways against the invasion of wasps. Extraordinary anecdotes are told of the prompt and ingenious use they make of this substance. Réaumur relates that, a snail having been observed by the bees on the window of the hive, they proceeded to glue the shell to the glass, and there sealed down the intruder in hopeless durance. In another case, that of a slug, the bees, having slain it with their stings, were quite unable to remove it from the hive. With wonderful foresight they then proceeded to secure their community from the noxious effects likely to arise from the decay of the carcase; and this they did by completely enveloping it with a coating of impervious varnish. Huish relates a similar occurrence in the case of a mouse caught in a hive by bees. Propolis yields benzoic acid, and contains some aromatic properties.