Cantharides (Gr. a beetle), coleopterous insects of several species, made use of in medicine. The most preferred is the can-tharis vesicatoria, procured mostly in the southern parts of Europe, but to some extent in all the temperate regions of Europe and western Asia. A species called the C. vittata, or potato fly, is common upon the potato plant of the United States; it is much used as a substitute for the foreign fly, being by many regarded as equally efficient, and is even adopted in the pharmacopoeias as officinal. Other species, too, are known in this country, and are in some parts exceedingly abundant. The potato flies appear on the plant in the mornings and evenings of August; during the day they disappear in the earth. They are collected by shaking them off into a basin of hot water. They are from one half to two thirds of an inch in length, and of a shining golden green color. - Cantharides are imported from the countries on the Mediterranean, and from St. Petersburg. The Russian flies, which may be distinguished from others by their superior size and peculiar copper hue, are the most esteemed. In the larva state the cantharides live in the ground upon the roots of plants.
The flies of southern Europe usually swarm upon the trees in May or June, selecting such as the white poplar, privet, ash, elder, etc. The early morning is the proper time for collecting them, when they are in a torpid state, and will easily let go their hold. Persons protected with masks and gloves beat the trees, and flies fall upon a linen cloth spread to receive them. They are then deprived of life by being exposed to the steam of hot vinegar. This method of destroying them dates back to the times of Dioscorides and Pliny. When dry they are carefully packed. If kept in air-tight vessels, they will retain their properties for many years; but if exposed, they will soon putrefy, particularly if reduced to powder. For this reason they should be kept whole until wanted for use. Being then powdered and mixed with ointment or lard, they make a valuable preparation for blistering plasters. Care is required in its application, as troublesome sores may follow its use. Internally administered, the medicine acts as a stimulant, principally upon the urinary and genital organs; its use is attended with danger, as in largo doses it acts as a powerful irritating poison.