Leeches are similar to earthworms, but instead of deriving nutrition from soil, most get it from blood. They do this by attaching themselves to their prey, making a miniscule slit in the skin and sucking the blood until they are full. Even predators can be preyed upon, however, and there are many animals that like to eat leeches.
Fish are the biggest natural predators of leeches and keep populations in check. An excessive number of leeches in a pond is an indication that there are not many fish. Nearly all freshwater fish will dine on leeches, but red-eared sunfish are known to have a special affinity for them and will eat them in massive quantities if given the opportunity.
Aquatic and semi-aquatic freshwater turtles, who spend a lot of time in the water, prey on leeches as an easy meal source. These include sliders, painted, map, mud, musk and snapping turtles. These turtles are omnivores and will eat both plant matter and meat, and leeches make up only a small part of their diet, which also includes algae, insects, duckweed, earthworms, frogs and small fish.
Birds that regularly prey on insects and fish also prey on leeches. Like turtles, the leeches normally make up only a small portion of a bird's diet but can be an important source of protein. Ducks are among the largest avian predators of leeches. They regularly dive to snap up the small creatures along with small fish, insects, snails and plant matter.
Saltwater and Land Leeches
Although not as common, some leeches live in saltwater and others live on land in moist areas. These leeches are preyed on by just about any omnivorous animal that normally eats small fish or insects, such as grouper, eels and puffer fish in the ocean and robins, monkeys and lizards on land.
Not every leech sucks blood, but most do, and they are not picky about their prey. Just because the victim is one of their natural predators, it doesn't stop leeches from attaching themselves and feeding on an animal that would otherwise eat them. Leeches prey on fish, turtles and birds as well as mammals that enter their territory, including humans. Some leeches will even prey on each other, sucking the blood from a fellow leech that has recently engorged itself.
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