Fig. 55.—A leech-farm in the south of France.
Leech-farming used to be a profitable undertaking, but now it has fallen into desuetude in these islands. Leeches are, however, still cultivated in some parts of the world; and in America, Latter describes a farm, situated at Newton in Long Island, where there is, or was, a leech-farm some thirteen acres in extent. The farm consists of oblong ponds of about one and a half acres, each three feet deep. The bottom of each pond is covered with clay, and the banks are made of peat. The French writers recommend, as a rule, the use of clay for the banks. The ‘eggs’ (cocoons) are deposited in the peat from June onwards, till the weather gets chilly. The adult leeches are fed every six months with fresh blood placed in stout linen bags suspended in the water. A more cruel method of feeding these domesticated leeches is that of driving horses, asses, or cattle into the ponds—and this was the custom in France.
Fig. 56.—Glossosiphonia heteroclita, with eggs and emerging embryos. Ventral view. × 4. (From Harding.)
Fig. 57.—Helobdella stagnalis, with adhering young. Ventral view, magnified. (From Harding.)
Some leeches show a considerable amount of maternal affection. Glossosiphonia heteroclita, for instance, carries its eggs about with it, and Helobdella stagnalis has its little young larvae attached by their tiny suckers to the mother’s body, which they are loath to leave.
Aulostoma gulo, the horse-leech, is notoriously a very ferocious feeder. Exactly why this species is called a horse-leech is a matter of speculation; but ‘horse’ used as an adjective seems to imply something large and something rather coarse—for instance, horse-chestnuts, horse-play, horse-sense, and horse-laugh.
The rapacity of the daughters of the ‘horse-leach’ is dwelt on in the Bible.[16] I am not an authority on exegesis, but I have never felt quite sure whether these two ladies were not the offspring of the local veterinary surgeon. But Aulostoma does occur in Palestine, and its voracity may very well have been known to the Hebrews. I entirely reject the idea that the word indicates some ghost or phantom: that explanation is due to the craven policy of taking refuge in the unknown.