These are a group of predatory worms (annelids, related to earthworms), one type of which attacks mammals. They lie on shallow, mucky (not sandy) bottoms in quiet water and react to moving shadows by swimming towards the shadow-casting object. Their bite is totally painless and non-toxic because the saliva includes anesthetics, anticoagulants, and powerful antibiotics, all of considerable interest to science. They feed for 20 to 40 minutes before dropping off, but may be removed by a steady pull at any time. The wound will continue to bleed and needs a band-aid. Their abundance varies greatly from year to year, with most years at Lake Sagamore being leech-free. Leeches are actively hunted by fish, turtles, and diving birds. There is no effective repellent, but swimmers (unlike waders) are seldom attacked.