THE WHITE MULBERRY.
(Morus alba.)
In Italy, where great attention is paid to the cultivation of the silkworm, the eggs are hatched in a room heated by a stove, and the young caterpillars are then removed on their mulberry-leaves to a cooler apartment called the nursery, where they are managed with great care and skill. Wicker shelves are arranged in the room at convenient distances, and are lined with paper, on which the worms are placed. Care is taken to place together only such worms as are hatched at the same time, for without this precaution the treatment, with respect to food, could not be regulated, and the moultings would not take place at the same time. Great care is also taken to secure the worms from rats and mice, as well as from certain insect enemies.
Silkworms are so little disposed to wander away from their food that open trays are sufficient to secure them: but unless great cleanliness is observed in their management, and frequent change of food given, a sickly smell is observed, and the caterpillars languish and die in great numbers. Supposing the young brood goes on well, and is properly attended by the child whom we have supposed to undertake the charge, there will be about five or six days’ feeding, and then the worms will begin to sicken for their first moult, or casting the skin. Silkworms have four of these moults, at each of which they appear to suffer pain or inconvenience; they also entirely leave off eating for two or three days. The caterpillars at that time raise the fore part of their bodies, and show tokens of uneasiness. They have grown rapidly, and their skins, not having grown in proportion, now appear to press and inconvenience them; but after two or three days fasting, they become thinner and are able gradually to rid themselves of their skin. It is now that their owner may see the use they begin to make of their silk. By watching them closely he sees each caterpillar throw out a number of very fine silken lines, by which it fastens the skin to one spot. Having done this, it is able to creep out, without dragging the skin about after it, as would otherwise be the case. In this operation the whole covering of the body, including that of the feet, of the jaws and teeth, is cast off; but it sometimes happens that the animal cannot entirely cast its skin, a portion of it breaking and remaining attached to the extremity of the body. As the animal increases rapidly in size, this portion of the old skin compresses its body tightly, causing inflammation and much suffering, which usually ends in death.
Worms that have newly moulted are readily distinguished by their pale colour, and the wrinkled appearance of the new skin. Soon after moulting they recover health and vigour, and feed with increased appetite. To keep them in health they must be fed with great regularity, and not crowded together in their trays. In the course of five days the rapid growth of the insect causes the wrinkles to disappear from the skin; it is now half an inch in length; a second sickness, and a second moulting, prepare it for increase of growth; it casts its skin as before, and feeds without intermission during another five days, during which time it attains a length of three quarters of an inch. It then falls sick and moults a third time. It again feeds during five days, after which it casts its skin for the fourth and last time in the caterpillar state.
PROGRESSIVE GROWTH OF THE SILKWORM.
It is now about one and a half or two inches in length, and devours its food most voraciously, increasing rapidly in size during ten days. When the worms are fed a slight hissing noise is heard similar to that of green wood burning. According to some writers this noise proceeds from the action of the jaws, but others attribute it solely to the action of the feet, which are continually moving until the worms have fastened to their food, when the noise ceases. In a large nursery of silkworms this noise sounds like a soft shower of rain.
SILKWORM ON MULBERRY-LEAF.