Oligochaetes as a Food Resource of Lake-Dwelling Leeches

Erpobdella octoculata, Glossiphonia complanata and Helobdella stagnalis were collected from the stony littoral of four productive and four unproductive English lakes at monthly intervals over one year. A serological technique, the precipitin test, was used to identify the presence of lumbriculid, naidid, tubificid and enchytraeid oligochaetes in the gut of the leeches. The proportion of total worms in the diet of Glossiphonia was greater in unproductive than productive lakes. For each of Erpobdella and Helobdella the proportions were similar. The families most extensively eaten by the leeches were tubificids in productive and lumbriculids in unproductive lakes. No and only a few enchytraeids were recorded in leeches from productive and unproductive lakes respectively. The remaining two worm families, in each lake type, were eaten in similar proportions. For each leech species, dietary composition did not change with increasing body size or with season. Feeding intensity peaked in mid-summer and mid-autumn, and was lowest in winter. It is concluded that the three leeches do not partition, in terms of families, the oligochaete resource.