Encyclopædia Britannica, Ninth Edition/Cantharides
CANTHARIDES, or Spanish Flies, are the common blister-beetles (Cantharis vesicatoria or Lytta vesicatoria) of European pharmacy. They are bright iridescent golden - green or bluish-coloured insects, with the breast finely punctured and pubescent, head and thorax with a longi tudinal channel, and elytra with two slightly elevated lines. The insect is from half-an-inch to an inch in length, and from one to two lines broad, the female being broader in the abdomen and altogether larger than the male. It is a native of the South of Europe, being found in Spain, France, Germany, Italy. Hungary, and the South of Russia, and it is also obtained in Siberia. The Spanish fly is also occasionally found in the South of England. The insects feed upon ash, lilac, privet, and jasmine leaves, and are found more rarely on elder, rose, apple, and poplar trees. Their presence is made known by a powerful disagreeable odour, which penetrates to a con siderable distance ; and people sitting under trees on which the insects were feeding have been known to be injuriously affected by their presence. They are collected for use at late evening or early morning, while in a dull bedewed condition, by shaking them off the trees or shrubs into cloths spread on the ground; and they are killed by dipping them into hot water or vinegar, or by exposing them for some time over the vapour of vinegar. They are then dried and put up for preservation in glass-stoppered bottles; and they require to be very carefully guarded against mites and various other minute insects to the attacks of which they are peculiarly liable. Mr H. Pock- lington has discovered by means of spectroscopic observa tions that the green colour of the elytra, &c., is due to the presence of chlorophyll; and he has demonstrated that the variations of the spectral bands are sufficient, after the lapse of many years, to indicate with some certainty the kind of leaves on which the insects were feeding shortly before they were killed. Cantharides owe their value to the presence of a peculiar chemical principle, to which the name cantharidin has been given. It is most abundant in large full-grown insects, while in very young specimens no cantharidin at all has been found. From about one-fourth to rather more than one- half per cent, of cantharidin has been obtained from different samples ; and it has been ascertained that the hard parts of the insect contain about six times more of the active principle than the soft parts. Cantharidin crystallizes in colourless four-sided prisms ; in solution or prepared with lard it produces very powerful vesication, and taken internally it is a violent irritant poison. Spanish flies are most largely used as an external application, being but rarely taken internally. They are applied as a topical stimulant for indolent ulcers, as rubefacients, and especially for blistering in inflammatory diseases. Taken internally in the form of tincture, they have been used in dropsy, in paralysis of the bladder, and for pro ducing aphrodisiacal effects. They have also been employed in lepra and other skin diseases ; and they have had a reputation in hydrophobia and other nervous disorders which they do not deserve.
A very large number of other insects belonging tj the family CantJiaridce possess blistering properties owing to their containing cantharidin. Of these the most remark able is the Telini fly of India (Jfylabris cicJtorii), the range of which extends from Italy and Greece through Egypt and Central Asia as far as China. It is very rich in cantharidin, yielding fully twice as much as ordinary cantharides. Several green-coloured beetles are, on account of their colour, used as adulterants to cantharides, but they are very easily detected by examination with the eye, or, if powdered, with the microscope.