What Is Parasitism? Definition, Types and Examples

Parasitism is a kind of symbiosis, a close and continuous long-term biological relationship between two species, where one organism, the parasite, lives on or inside another organism, the host. The parasite may have a negative impact on the host’s health and is adapted structurally to this way of life. Parasitism is found in a variety of organisms, including plants, animals, and microorganisms.

Parasitism Definition

Parasitism is a ecological interaction between two different species where one species known as the parasite, benefits at the expense of the other species, known as the host.

What is Parasitism?

In parasitism interaction, the parasite derives various resources, such as nutrients, shelter, or a place to reproduce, from the host, often causing harm or damage to the host in the process. The majority of the parasites harm the hosts because the parasites live by getting nutrition from the body of the host which disturbs the host’s growth and reduces its survival and reproduction capacity of the host which results in a decline in its population density. The parasites make the host more vulnerable to predation by making it physically weak.

Parasites have evolved to be host specific that is they depend on only specific types of organisms. They are able to parasitize only specific types of hosts. Generally host organism develops some methods for resisting the parasite but the parasite in counter to the host also develops methods to adapt to the environment such as loss of unnecessary sense organs or suckers to cling to the host, loss of the digestive system, and high reproductive capacity.

Types of Parasitism

Parasitism represents a biological interaction where one organism, referred to as the parasite, gains advantages while causing detrimental effect on the another organism known as the host. Various types of parasitism are determined by the nature of interaction between the parasite and the host, theses are as follows:

Ectoparasitism

Ectoparasitism is a interaction in which parasitic organisms reside externally on the host’s surface. These organisms are present in various forms, including insects like fleas, ticks, lice, mites, and select worms. Ectoparasites negatively effect the host by feeding on its blood, skin, or bodily secretions.

Endoparasitism

Endoparasites is a type of interaction in which parasite resides within the host’s body. They inhabit various internal organs or tissues of the host, such as the circulatory system, digestive system, etc. Examples of endoparasites includes roundworms, tapeworms, and specific protozoa.

Brood Parasitism

In the brood parasitism parasitic organisms lay their eggs in the nests of host species and the host species then incubates and raises the parasite’s offspring, often at the expense of their own young. Example is the cuckoo bird, which lays eggs in the nests of other bird species.

Facultative Parasitism

Facultative parasites have the flexibility to switch between a parasitic form and a non-parasitic (free-living) form based on environmental conditions or other factors. They can survive and obtain nutrients from both host organisms and alternative food sources, such as decaying organic matter.

Organisms exhibiting facultative parasitism often have complex life cycles that involve both parasitic and non-parasitic stages. Examples: Some fungi, like certain species of Cordyceps, are facultative parasites that can infect insects or other arthropods but can also grow saprophytically on dead organic matter.

Obligate Parasitism

Obligate parasites are entirely dependent on a host organism for their survival, reproduction, and nutrient . They cannot live independently. They possess specialized adaptations such as hooks, suckers, or enzymes that facilitate attachment to the host and extraction of nutrients from the host.

Unlike facultative parasites, obligate parasites cannot switch to a non-parasitic form or feed on alternative food sources. They rely exclusively on their hosts. Examples: Internal parasites like tapeworms, which inhabit the digestive tracts of their host animals, are obligate parasites. They lack the ability to live outside of a host organism. Many blood-feeding parasites like mosquitoes or ticks are also obligate parasites, as they require a host’s blood for sustenance and reproduction.

Meso Parasitism

Meso parasitism is a parasitic relationship where one parasite targets another parasite within a host organism. It involves three organisms: the primary host, the primary parasite, and the secondary parasite. The secondary parasite exploits the primary parasite, benefiting at its expense. Example: When a secondary parasite attacks a host already parasitized by a primary parasite.

Examples of Parasitism

Parasitism is a type of symbiotic relationship in which one organism benefits at the expense of another organism. The association may also lead to the injury or death of the host. The various examples of parasitism in humans, plants and insects are as follows:

Parasitism in Humans

Parasitism in humans involves various organisms that exploit the human body for their benefit, often causing harm to the host. For examples:

• Malaria (Plasmodium spp.): Plasmodium parasites transmitted by mosquitoes cause malaria in humans, leading to symptoms like fever, anemia, and organ damage.
• Tapeworms (Taenia spp.): These flatworm parasites can infect the human digestive tract, where they absorb nutrients from the host’s food, potentially causing weight loss and other health issues.
• Head Lice (Pediculus humanus capitis): These ectoparasites infest the human scalp, feeding on blood and causing itching and discomfort.

Also Read: Human Digestive System

Parasitism in Plants

Parasitism in plants involves various parasitic plants that derive nutrients from other host plants. For example

• Dodder (Cuscuta spp.): Dodder is a well-known parasitic plant that lacks chlorophyll and attaches to the host plant, depriving it of nutrients.
• Broomrape (Orobanche spp.): Broomrape is another root-parasitic plant that attaches to the roots of various host plants, causing stunted growth and reduced yield.
• Mistletoe (Viscum album): Mistletoe is a partial stem parasite that grows on trees and shrubs, extracting water and nutrients from the host plant.
• Hydnora africana: This subterranean parasitic plant attaches to the roots of other plants, relying on them for nutrients. 

There are two types of parasites in plants:

• Hemi Parasitic plant (Hemi parasites can photosynthesize but also drain water and nutrition from their hosts.)
• Holo Parasitic plant ( Holo parasites cannot photosynthesize and depend on their hosts for food.)

Also Read: Photosynthesis

Parasitism in Insects 

Parasitism is a common occurrence in the insects, and many species of insects are either parasites or hosts to other insects. Parasitism in insects is a common ecological phenomenon where one insect species, the parasite, benefits at the expense of another insect species, the host.

• Parasitic Wasps: Many parasitic wasps lay their eggs on or inside other insects, such as caterpillars. The wasp larvae consume the host insect from the inside.
• Fleas: Fleas are external parasites that infest mammals, including pets and humans, feeding on their blood.
• Lice: Lice are ectoparasitic insects that live on the skin and feathers of birds or the hair of mammals, including humans.
• Ticks: Ticks are ectoparasites that attach to the skin of mammals and birds, feeding on their blood and transmitting diseases.

FAQs on Parasitism

1. What is parasitism?

Answer:

Parasitism is a biological relationship between two organisms, where one organism, known as the parasite, benefits at the expense of the other organism, called the host. The parasite derives nutrients and sometimes shelter from the host, often harming or weakening it in the process.

2. How do parasites harm their hosts?

Answer:

Parasites can harm their hosts in several ways. They may consume the host’s tissues or bodily fluids, disrupt the host’s normal physiological functions, weaken the host’s immune system, or compete for resources like nutrients.

3. What are some examples of parasites?

Answer:

Examples of parasites include ticks, fleas, tapeworms, leeches, and various microorganisms like malaria parasites and tapeworms in humans.

4. What are the benefits of parasitism?

Answer:

Some parasites can have ecological benefits. For example, parasitoid wasps can help control pest populations by laying their eggs inside other insects, ultimately killing the host and reducing pest numbers. Additionally, some parasites have been studied for their potential in medical treatments and research.

5. What is the study of parasitism?

Answer:

The study of parasitism is known as “parasitology.” Parasitology is a branch of biology that focuses on the study of parasites, their hosts, and the interactions between them.