Growth of the medicinal leech, Himudo medicinalis, under natural and laboratory conditions

SUMMARY 1. The growth of the medicinal leech, Hirudo medicinalis L., was studied in the wild by a mark and recapture technique, and in the laboratory. Growth in the wild, even after 2 years, was generally small and variable. 2. After being offered regular feeds of various preparations of bovine blood through a pig-ileum membrane and being allowed to feed to satiation, hatchling leeches in the laboratory showed a saltatory pattern of weight gain with increases greatly in excess of those seen in the wild. Twelve of twenty-five leeches starved from hatching survived for about 250 days. The ability to survive for long periods without feeding may well be important for the overwintering survival of late hatchlings.