CHAPTER IX.
OTHER INSECT PRODUCTIONS USEFUL TO MAN.
Almost any article could be better spared from the materia medica, than an insect remedy called cantharides, or Spanish flies. This consists of the bodies of small beetles, in which resides an active blistering principle of great importance, not only as an external application, but also sometimes as an internal remedy. The insect chiefly used in Europe is the cantharis vesicatoria, for the most part rare in England, but seen on some occasions in great numbers, as in the summer of 1837 in Essex, Suffolk, and the Isle of Wight. Other insects of the same family are employed in foreign countries.
The true blistering beetle has complete wings and wing cases; its body is long and narrow, varying in size, but in general about nine lines long and two or three lines wide. It is of a rich green and golden colour, very shining and delicately tinctured, with the antennæ black, except the first joint.
“The cantharis is one of those insects which have been most anciently and most universally known. Physicians, who were the first natural philosophers, and the first observers of nature, have made mention of the cantharides in the remotest times. But they have only considered them under that relation which was most suitable to their own profession, and as furnishing to medicine one of its most powerful agents. The naturalist, who is less anxious about becoming acquainted with the medicinal virtues of the dead, than with the peculiar habits of the living cantharides, is yet very far from having acquired in this respect extensive and satisfactory information. The only species which has been deemed to be endowed with useful properties, has caused a forgetfulness of all the others which compose the entire genus; and all that we know in general respecting these insects, is that in our European climates they live on plants, devour the leaves of certain trees, shun the cold, appear at the commencement of spring, and disappear at the beginning of autumn. * * * It is more than probable that experiments on insects relatively to their utility in medicine and the arts, have been too much neglected in general. Their diminutive size has doubtless caused them to be too much despised. It cannot however be doubted, that there must be a great number of them whose virtues are at least equal to those of the cantharides, and many others which are less acrid and less caustic might in many cases be taken internally, with less danger and a greater chance of success.”
The early history of this insect is not well known. The female buries her eggs in the ground; the larvæ have a soft body of a yellowish white colour; they live in the earth, and feed on various roots. When full grown they change into the nymph state in the earth, and do not emerge from it until they have assumed the perfect insect form.
They are very abundant in Spain and in the South of France, especially in June, when they assemble in swarms. This is the time for gathering them, and the hour of sunset or sunrise is chosen for the purpose, as they are then in a somewhat torpid state. They are found upon ash-trees, honey-suckles, lilacs, rose-trees, poplars, elms, &c., the leaves of which they devour, and when this food fails they attack corn and grass, and do much damage. The swarms are preceded by a fœtid odour resembling that of mice. They are gathered in various ways; the most simple is to spread cloths under the tree upon which a swarm has settled, and then to shake them down; they are afterwards collected upon a hair sieve, and held over the vapour of boiling vinegar, which kills them; or the cloth in which they are collected may be folded loosely up and dipped in vinegar, which has the same effect. Another method is to boil a quantity of vinegar under the tree where they are collected, and the ascending vapour kills them.
The particles emitted by these insects are so very corrosive that persons are liable to be violently affected who attempt to gather them with bare hands during the heat of the day. It is also dangerous to be under a tree where a swarm has gathered. Persons who collect them should always wear a mask and gloves.
After the insects are killed they must be dried; this is done in the sun or in a heated room, upon tiles covered with cloth or paper. They are moved about from time to time with a stick, or with the hands furnished with gloves. When properly dry they are so light that fifty weigh scarcely a drachm.
They are packed in boxes or barrels lined with paper and perfectly dry. If damp gets to them they contract a detestable odour, and are unfit for use.
A portion of our supply of cantharides is from Astracan and Sicily: but the greatest quantity is from St. Petersburgh, the Russian insects being superior to those of Sicily and France.