All About Parasites

A parasite is a plant or animal that lives in or on some other living thing and gets food from it. "Parasite" comes from the Latin for "beside food."

The plant or animal that supports a parasite is called a "host." A parasite's host may have to be a certain kind of living thing. For example, beechdrops, a plant parasite, can live only on the roots of beech trees. Other parasites follow the old saying that "beggars cannot be choosers." It makes no difference to a wood tick, for instance, whether it gets a meal from a man or a dog. Many kinds of dodder will grow on any green plant within reach.

In the course of their lives some parasites have to have more than one host. The tiny one-celled animal that causes malaria must spend part of its life inside a human being and part inside a mosquito.

Many parasites get shelter as well as food from their hosts. A tapeworm lives its whole life inside the body of the animal it gets food from. A flea does not live inside the dog that furnishes it with food, but the dog's thick hair shelters it.

A parasite may not stay with its host all the time. A wood tick ready for a meal crawls up on a small plant. It clings to some animal that brushes against it. It pushes its beak into the skin of the animal and begins filling itself with blood. Perhaps for as long as a week it rides about, taking in as much blood as it can hold. Then it drops off into the grass to digest its big meal.

Some living things are only partial parasites. Mistletoe is one. It perches high on trees and sends roots into them. But it takes nothing but water from the trees. It can make the rest of its food with its leaves.

In the plant kingdom the biggest number of parasites is found in the group called the "fungi." By no means all fungi are parasites, but many are. Much harm is done to both plants and animals by such fungus parasites as rusts and disease bacteria. In the animal kingdom the parasites are scattered among many groups. There are worms, insects, mites and ticks, tiny animals called protozoa, and others.

Being a parasite is not at all an unusual way of getting a living. No large plant or animal escapes having parasites. Most small plants and animals have parasites, too. As a rule, even a parasite is a host to still smaller parasites. A flea, for example, sucks the blood of a dog. In the flea's body there are likely to be some tiny worms. In the bodies of the worms there are likely to be some tiny one-celled animals. And inside these tiny animals there are likely to be bacteria.

Source: "Parasite," Microsoft Encarta Online Encyclopedia