What Are the Functions of Parasites?

If your pet has ever suffered from tapeworm or if you've ever had giardia, you may find yourself wondering why parasites exist in the first place. Annoying as they may be, parasites do have functions in the natural world and are a part of ecosystems whether we like them or not.

Regulating species population

• Like disease and natural disasters, parasites regulate the population of any given species at any given place and time. Without parasites, a species might proliferate to the point where its ecosystem cannot sustain it. Thus, one of the purposes of parasites is to create balance within ecosystems. Imagine, for example, a herd of cattle that is grazing to the point that there is hardly any more vegetation. A parasite can limit their numbers.

Parasites and the food web

• The old model of the top-down food chain is transformed into a web by the addition of parasites. Animals at the "top" of the food chain, predators, are most susceptible to parasites, which reach them through the animals they eat. Studies have shown that there are more links in the food web between parasites and hosts than between predators and prey. In this way, parasites contribute to the stability of the food web.

Getting rid of decomposition

• Some parasites feed on decomposing flesh, which aids in the natural decomposition of, say, the dead squirrel in your front yard. Especially in natural settings, this aid in decomposition is important. In some hospital settings, parasites can be used to get rid of rotting flesh to speed the natural process of healing from a burn or sore. It's important to note, however, that this isn't something to try at home.

Bolstering immunity

• Some recent studies have suggested that parasites actually play an important role in immune function, and speculate that the rise of autoimmune disorders in modern societies may be due to their effectiveness in getting rid of parasites. A scientist at the University of Iowa showed that some worms calmed the immune system, even though when their numbers got too high they caused anemia and other problems. He rationalized that the parasite functions to keep its host healthy for its own sake in a relationship that blurs the line between symbiotic and parasitic.