The word parasite is derived from the Latin form of the Greek word, meaning “one who eats at the table of another”. Parasitism is generally defined as a relationship between the two living species in which one organism is benefitted at the expense of the other. The organism that is benefitted is called the parasite, while the one that is harmed is called the host.

A few examples of parasites are tapeworms, fleas, and barnacles. Tapeworms are flatworms that are found attached to the insides of the intestines of animals such as cows, pigs, etc.. They feed on the host’s partly digested food, depriving it of the nutrients.

There are various types of parasitism and are classified based on their size, characteristics, interactions with their hosts and their life cycles.

This is the kind of parasitism in which the parasite is completely dependent on the host to complete its life cycle. Obligate parasites cannot survive without the host. Therefore, they do not severely harm the host. Fungi, bacteria and viruses exhibit obligate parasitism. For eg., head lice, when removed from the human scalp, dies.

In this kind of parasitism, the parasite is not completely dependent on the host to complete its life cycle and can survive without the host. A nematode species Strongyloides stercoralis is found free-living but causes a disease strongyloidiasis when it infects humans.

The parasites that live outside the body of the host exhibit ectoparasitism. For eg., lice and ticks

Parasites that live inside the body of a host exhibit endoparasitism. For eg., hookworms and nematodes.

The parasites that enter the external openings of the host exhibit mesoparasitism.

There are many examples of parasites, as it is a type of interaction between the two species. Listed below are some of the common examples of parasitism.

The organisms that parasitize humans include fungi, leeches, lice, viruses, protozoa, tapeworm, etc. Few organisms such as Helminthes live inside the intestine of the host and causes several infectious diseases, such as jaundice, malnutrition, diarrhoea, etc. All the infections are caused by viruses and bacteria.

Small green insects called aphids, parasitize plants by eating their sap. Several types of fungi parasitize crops ad spoil fruits, vegetables and food grains. The parasitic plants contain modified roots called haustoria which connect to the host xylem or phloem and drain it of nutrients and water.

Parasitism is very common in insects. Entomophagous parasites attack larva and young insects. A few insects deposit their eggs within the body of the larva of other insect species. When the eggs hatch, the young one eats the larva and derives nutrition from it.