In using cantharides they are reduced to powder, mixed with some fatty substance, and applied in the form of a plaster to the surface of the body: it begins to act immediately, and separates the outer skin from the dermis with great rapidity.
A singular employment of insects in the composition of soap is made in some parts of Africa. Geoffrey the younger relates, that being at the village of Postudal, some leagues from Senegal, in search of insects, one of the negroes whom he had employed in the same pursuit brought him a vessel containing an immense quantity of a small species of carabus, and informed him that this insect entered into the composition of the soap used in that country; at the same time he exhibited a ball of a dark-coloured soap, the properties of which are similar to the soap used in Europe. It appears that the insect abounds in alkali, which makes it useful for the purpose in question.
The following figure of the soap insect (Carabus saponarius), is copied from M. Olivier’s large work on insects.
Another useful insect substance is a kind of resin, or more properly speaking, wax, which by adulteration with a resinous substance is made heavier for the market. This is found in the province of Coquimbo, South America, and is the production of a caterpillar, which feeds on a shrub called chilca, a species of origanum. The caterpillars are of a red colour, and about half an inch in length. They appear in great numbers in the beginning of the spring on the branches of the chilca, where they form their cells of a kind of soft wax. In these they become changed into a small yellowish moth, with black stripes upon the wings. The wax is at first very white, by degrees becomes yellow, and finally brown; this change, and the bitter taste which it acquires, is supposed to be owing to the fogs which are very frequent in the provinces where it is found. It is collected in autumn by the inhabitants, who boil it in water, and afterwards make it up into little cakes, in which form it is brought to market. In order to increase its weight, many are accustomed to mix it with the resin obtained from another resinous shrub, and in this state great quantities are sold to ship-masters, who use it for paying their vessels.
Upon the branches of the wild rosemary is also found a whitish viscous substance, in globules of the size of a hazel-nut, containing a very limpid oil, which proceeds from the shrub. These glands serve for the habitation of a kind of caterpillar, which becomes transformed into a small fly, with four brown wings, of the genus Cynips.
The foregoing details will be sufficient to show that we are indebted in no small degree to the labours of insects for comfort, convenience, and health. It becomes us then to receive not unthankfully the benefits they confer, while we view them as the agents of a higher power, under whose direction they work with ceaseless activity in their humble sphere, and produce results, not less astonishing in themselves, than valuable and beneficial to mankind.
LONDON