All about leeches

Abstract

Most people think of leeches as nasty bloodsucking creatures with little or no worth, and no interesting behaviors, let alone any parenting skills, but this popular perception of them is way off the mark. A common misconception about leeches is that there is only one kind of leech. In fact, there are between 700 and 1000 species of leeches worldwide and they can be found in a variety of different habitats including marine, estuarine, moist terrestrial (particularly in Australia and Southeast Asia) and freshwater ecosystems. Within these habitats, leeches can be found attached to various substrates including fish and other marine creatures (marine and estuarine), underneath rocks or clinging to vegetation (moist terrestrial), or living on submerged wood, stones, and aquatic vegetation in ponds, streams, and rivers. Even if you know where to look for them, leeches can still be difficult to find since many species are often well camouflaged, blending in perfectly with their environment and making them extremely hard to locate. Despite their close association with medieval medicine, leeches today are used for a variety of medical purposes including providing useful treatments for arthritis, blood-clotting disorders, varicose veins and other circulatory disorders and are also used in modern plastic and reconstructive surgery. In addition to their medical uses, leeches are quite fascinating in their own right and have some very interesting behaviors. For instance, it turns out that many leech species are very good parents, caring for their young in a manner that resembles the care shown by birds or even mammals. They can care for their young in a variety of ways including building nests for them, carrying broods of eggs or young attached to their ventral surface, or even, in several species, carrying the eggs and young in an internal pouch (like a marsupial). In quite a few cases, the parent leech also feeds its young, either directly providing nutrients across the body wall or, more frequently, by capturing and killing prey for the youngsters to feed on until they are big enough to provide for themselves. What do leeches eat? Contrary to popular belief, not all of them are bloodsuckers. In fact, many of them are sit-and-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) or they are equipped with a protrusible proboscis which resembles a hypodermic needle. 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