Contrary to popular belief, not all leeches are bloodsuckers. In fact, many of them are sitand-wait predators and feed on a variety of different invertebrates such as insects (gnats, mosquito larvae, water bugs), oligochaetes (both aquatic blackworms and their terrestrial cousins, the earthworms), amphipods (side-swimmers), and lots of different kinds of molluscs including pond snails and freshwater clams. These predacious leeches are either engulfers (ie. they swallow their prey whole) like the Montezuma Well endemic Motobdella montezuma, or they are equipped with a protrusible proboscis which resembles a hypodermic needle. The four species of Helobdella found in Montezuma Well all feed by means of a proboscis. When not in use, the proboscis is retracted into the mouth, but when a leech has located a prey item, the proboscis pops out of the mouth and the leech uses it to spear its prey and then, once the prey is subdued, the leech uses the hollow proboscis like a soda straw and sucks up the juices of its prey. Some proboscis leeches and another type of leech (with jaws instead of a proboscis are temporary ectoparasites on a variety of different vertebrates including fish, turtles,crocodiles, and humans.
These are the bloodsuckers and are the ones that most people think of when the word “leech” is mentioned. They don’t need much introduction since they are infamous in their own right, having had starring roles in movies such as the Hollywood classic, African Queen, and, more recently, Stand by Me and even the BBC television comedy Black Adder. Many bloodsuckers have jaws instead of a proboscis with which to bite their hosts and depending on which family the bloodsucker belongs to, they can have either two or three jaws. The jaws look like tiny half circular saw blades, are extremely sharp, and come equipped with either tiny pointed teeth or a cutting edge. The two-jawed kinds leave a V-shaped bite and the three-jawed ones leave a Y-shaped bite. Bloodsucking or sanguivorous (blood-feeding) leeches will readily feed on fish, reptiles (turtles and crocodiles), amphibians (frogs), waterfowl (ducks, etc.), and mammals including humans, but when larger prey are scarce, they have been known to feed on earthworms or other available invertebrates to tide them over until their next blood meal. Fortunately, none of the leeches that live in Montezuma Well are bloodsuckers. Instead, they all feed on invertebrate prey and are are quite harmless to humans. Besides feeding on everything from snails to humans, leeches themselves are often preyed upon by other organisms and can form an important part of the diet of some other aquatic predators including other invertebrates such as dragonfly or damselfly nymphs and vertebrate predators such as fish and ducks