It is hard to see the Cotton-bees in action, since they work inside the reeds when making the nests. However, I will describe the little that I saw. The Bee procures her cotton from many different kinds of plants, such as thistles, mulleins, the woolly sage and everlastings. She uses only the plants that are dead and dry, however, never fresh ones.
In this way she avoids mildew, which would make its appearance in her nests in the mass of hairs still filled with sap.
She alights on the plant she wishes to use, scrapes it with her mouth, and then passes the tiny flake to her hind-legs, which hold it pressed against the chest, mixes with it still more down, and makes the whole into a little ball. When this is the size of a pea, it goes back to the mouth, and the insect flies off, with her bale of cotton in her mouth. If we have the patience to wait, we shall see her coming back again and again to the same plant, until her bags are all made.
The Cotton-bee uses different grades of cotton for the different parts of her work. She is like the bird, who furnishes the inside of her nest with wool to make it soft for the little birds, and strengthens the outside with sticks. The Bee makes her cells, the grubs’ nurseries, of the very finest down, the cotton gathered from a thistle; she makes the barrier plug at the entrance of stiff, prickly hairs, such as the coarse bristles scraped from a mullein-leaf.
I do not see her making the cells inside the bramble, but I catch her preparing the plug for the top. With her fore-legs she tears the cotton apart and spreads it out; with her jaws she loosens the hard lumps; with her forehead she presses each new layer of the plug upon the one below. This is a rough task; but probably her general way of working is the same for the finer cells.
Some Cotton-bees after making the plug go even further and fill up the empty space at the end of the bramble with any kind of rubbish that they can find: little pieces of gravel, bits of earth, grains of sawdust, mortar, cypress-catkins, or broken leaves. The pile is a real barricade, and will keep any foe from breaking in.
The honey with which the Cotton-bee whose nest I examined filled the cells was pale-yellow, all of the same kind and only partly liquefied, so that it would not trickle through the cotton bag. On this honey the egg is laid. After a while the grub is hatched and finds its food all ready. It plunges its head in the honey, drinks long draughts, and grows fat. We will leave it there, knowing that after a while it will build a cocoon and turn into a Cotton-bee.
Another interesting Bee who uses a ready-made home is the Resin-bee. In the stone-heaps which have been left from the quarries, we often find the Field-mouse sitting on a grass mattress, nibbling acorns, almonds, olive-stones, apricot-stones, and snail-shells. When he is gone, he has left behind him, under the overhanging stones, a heap of empty shells. Among these, there is always a hope of finding a few plugged up with resin, the nests of this sort of Bee. The Osmia-bees also use snail-shells, but they plug them up with clay.