They have jaws which actually cut through skin to reach blood vessels and tissue. Not all kinds of leeches attract fish. The leech species that live in waters with gamefish populations usually make poor bait. Most game fish ignore horse leeches. Either the scent of the horse leech repels fish or it lacks the action of bait leeches.
Fish eat many types of leeches, but only the ribbon leech is widely used as bait.
A few anglers have found tiger leeches to be good panfish bait. A ribbon leech has a firmer body than a horse leech and body situations or grooves that are less pronounced. The color of a ribbon leeches varies from pure black to light brown. Some have a brown or olive background with many black spots. Leeches are easy to keep alive.