Parasitism - Definition, Types and Examples

Parasitism is a relationship between two species of animals or plants in which one benefits at the outflow of the other, sometimes without killing the host life form. Parasites will cause parasitism. 

Types of Parasitism:

Parasites can belong to various classifications based on their characteristics, size, and relationship with the host life form. There are different types of parasitism and they are as follows:

  • 1. Obligate Parasitism:

  • Obligate parasites are wholly reliant on the host organism in order for them to survive. Over time, they have developed so that they will be unable to complete their life cycle without the existence of the host organism. Since the parasites need to survive, they usually will not cause severe damage to the host, except the host's death is required for the transmission of the parasite. Obligate parasitism will be found in various types of living beings like animals, fungi, plants, viruses, and bacteria. Head lice will come under the category of obligate parasites, if eliminated from the human scalp, they will soon die.

  • 2. Facultative Parasitism:

  • In order to survive, the facultative parasites don’t rely on the host organism. They will be able to stay alive even without the host and only sometimes, perform the parasitic behaviors. Some fungi, plants, animals, and microorganisms will be facultative parasites. For example nematode species Strongyloides stercoalis, a type roundworm can cause a disease called Strongyloidiasis when it affects human beings, it can also be found to be free-living without the support of any host organism.

  • 3. Ectoparasitism, Endoparasitism, and Mesoparasitism:

  • Ectoparasites exist outside the body of the host life form such as ticks and lice. Endoparasites exist inside the body of the host such s hookworms and nematodes. Mesoparasites penetrate through the external openings of the host such as the outer ear of the cloaca.

  • 4. Epiparasitism:

  • An epiparasite parasitizes the other life form that is also a parasite. They are also known as secondary parasites or hyperparasites. An example of epiparasite is protozoan which lives in a flea that is surviving on a dog.

  • 5. Social Parasitism:

  • Social parasites benefit from social insects like bees, ants, and termites. They would make use of mimicry to attack the hive. Some bumblebees attack the hives of other species of bees, making those species grow the parasites young. An ant species called Tetramorium inquilinum, a parasite, spends its complete life cycle on the back of the other ant species, necessarily making the host organism to be its slaves.

    The parasite species has benefited in many ways such as transportation and food. Due to this form of extreme parasitism, the ants evolved to be so weak that if they happen to fall off from their host, they would not be able to edge back on, and so they will die.

  • 6. Brood Parasitism:

  • Brood parasitism engages the elevating of the young. Some bird species like cuckoos and cowbirds that practice brood parasitism will lay their eggs in the nest of other species instead of building their own nests. Here, the species that lay their eggs in that of the others nest gains benefits as they need not spend energy in raising their young ones while the other species are affected because they use their energy to raise the young one which is not of their genetic material. 

    Here, the parasite species will even lash out the other eggs of the other species out of the nest, forcing the host species to rise the young one of the parasites alone. In the species of fishes also brood parasitism occurs. A type of parasitism called kleptoparasitism directly or indirectly involves taking food from the host organism. Here, the food that would have gone towards the host species goes to the parasites instead.

    Examples of Parasitism:

  • 1. Parasitism in Human Beings:

  • More than 100 varieties of organisms can parasitize human beings including leeches, fungi, ticks, lice, protozoa, tapeworms, and viruses. The worms that live inside the intestines of human beings, called helminths can grow meters in length in the intestines. They will cause various problems like jaundice, malnutrition, and diarrhea and even cause the death of the host. On the other hand, they could be treated with anti-parasitic tablets. Many infectious diseases including the common cold will result from the organisms that parasitize human beings, for example, bacteria and viruses. Most of the organisms which parasitize human beings could also parasitize other birds and mammals.

  • 2. Parasitism in Plants:

  • Small green insects like aphids parasitize plants by feeding on their sap. Most f the types of fungi can also invade plants and ruin fruits, wheat and vegetables. Even some plants are parasites themselves. In flowering plants (angiosperms), parasitism has developed at least 12 separate times and nearly 1% of the flowering plants are parasitic. Haustoria, modified roots that connect to the host plant’s xylem or phloem will drain it of nutrients and water will be present in the parasitic plants.
  • 3. Parasitism in Insects:

  • The parasites that parasitize other insects are called Entomophagous parasites, which are also insects. Generally, the parasites invade young insects or larva. Some of the parasite insects dump their eggs within the body of another insect species' larva. When the eggs emerge, the parasitic young one kills and eats the larva, benefiting nutrients from the host larva. The parent parasite paralyzes the host which is then consumed by the young. Commonly, this occurs in wasps like Ampulex compressa, whose young eat paralyzed cockroaches which have been stung by the parent. Some wasps like Ropalidia romandi pierce into the abdomen of their host and survive there. Here, the parasites change their behavior and appearance and even make the host sterile but don’t kill their host species. Almost all insect species are attacked by at least one type of parasite.