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A Parasite is an organism that lives on the body or in the body of another organism that gets food from the organism in or on which it is present by harming it. 

Parasitism Definition

It is an interaction between 2 species in which parasites live liven in the host body, parasite benefits and the host is harmed due to this.Such type of interaction is known as Parasitism.

What is Parasitism?

Parasitism is a symbiotic relationship between two organisms in which one organism, called the parasite, benefits at the expense of the other organism, called the host. In a parasitic relationship, the parasite lives on or within the host, obtaining nutrients and shelter from the host. This can have a negative impact on the host’s health, potentially causing disease, discomfort, or death. Parasitism can be found in a variety of organisms, including plants, animals, and microorganisms. The parasitic mode of life ensures free lodging and meals.

Many 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 techniques for resisting the parasite but the parasite in counter to the host also develops techniques 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.

Example of Parasitism

An example of parasitism is the relationship between a flea and a dog. The flea feeds on the blood of the dog, obtaining nutrients and energy, while the dog experiences discomfort and potential health problems as a result of the flea’s feeding behavior. In this relationship, the flea is the parasite and the dog is the host.

Types of Parasitism

There are mainly five types of parasitism classified by the size, characteristics of parasites, and their interaction with their hosts.

Endo Parasitism

The parasitism in which parasites feed on the internal surface of the host organism is called  Endo parasitism


  • Malaria parasite which goes and lives inside the body of human being
  • Roundworms and tapeworms present in the human body 
  • Intercellular parasites
  • Nematodes and helminths present in the human body

Ecto Parasitism

Ecto Paraitism


The parasitism in which parasites feed on the external surface of the host organism is called Ecto parasitism.


  • Ticks, and fleas on dogs  
  • Copepods of marine fishes 
  • Head louse on children’s head
  • There is a particular plant called Cuscuta which generally grows on hedge plants deriving its nutrition from the hedge plant

Obligate Parasitism

The parasitism in which the parasite can not live without a host is called Obligate parasitism. Obligate parasites are completely dependent on their hosts to complete their life cycle. So obligate parasites will not kill their hosts. Because if there is no host obligate parasites cannot live and fails to reproduce. Obligate parasites are also called holo parasites.


 An example of obligate parasitism is the relationship between lice and humans. Lice are small insects that feed on the blood of their human hosts. They cannot survive without a human host and cannot feed on any other source of food. In this relationship, the lice are obligate parasites and the humans are the hosts.

Facultative Parasitism

Facultative parasitism is a type of parasitism in which the parasite can live either as a parasite or as an independent organism. Facultative parasites are able to switch between a parasitic and a non-parasitic lifestyle depending on environmental conditions and the availability of hosts.

Facultative parasitism is considered a flexible survival strategy, as the organism can adapt to changing conditions and still ensure its survival. However, facultative parasitism also poses a risk to the host, as the parasite may become a parasite when conditions are unfavorable for independent existence.


Mistletoe is a plant that can grow either as an independent plant using photosynthesis to produce its own food or as a parasite, obtaining nutrients and water from the sap of other trees. If mistletoe encounters a suitable host tree, it will grow as a parasite, attaching itself to the host tree and tapping into its sap. If the mistletoe does not encounter a suitable host, it will grow as an independent plant.

Meso Parasitism

Mesoparasitism is a type of parasitism in which the parasite lives within the host’s body but does not invade its tissues or cells. Mesoparasites are typically found in the host’s digestive or respiratory systems and feed on the host’s food or bodily secretions.


An example of mesoparasitism is the relationship between tapeworms and their hosts. Tapeworms are long, segmented worms that live inside the intestines of their hosts, including humans and animals. They feed on the host’s partially digested food and absorb the nutrients through their body surface. In this relationship, the tapeworms are meso parasites and the humans and animals are the hosts.

Brood Parasitism

Parasitism in which animals rely on other animals to raise their young ones is called Brood parasites. The animal which gives its young to raise to the host is called a Brood parasite. A Brood parasite manipulates the host animal to raise its young one as if it were its own child. This helps the brood parasite to get relieved from the work of raising their young ones and building homes in which they will use the time to produce more offspring.


When we see the nest of a crow, we can find the eggs of a cuckoo because a cuckoo will lay its eggs in the nest of a crow in order to get its young ones raised by the crow, and the crow will incubate its eggs and raise the cuckoo bird’s babies as if they were its own babies and cuckoos eggs have evolved in such a way that they resemble the crow’s eggs in size and color. 

Example of Parasitism

The following are the common example of parasitism: 

Parasitism in Humans

Tapeworms are a type of round flattened worms that sticks to the intestines of humans and which live on the partially digested food of the host organism (humans) which makes the host deprive of nutrients which results in the weakening of the host. This sometimes results in health problems in humans and sometimes abdominal pain, diarrhea, skin rashes …etc. They can be generally treated by taking a medicine called Albendazole which is well known to all.

Also Read: Human Digestive System

Parasitism in Plants

In plant Parasitism, Parasitic plants connect to the vasculature of a host plant and take part or all of the water, nutrients, and assimilates they need to complete their life cycle. 

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

Nematodes – also known as roundworms – exist in almost every environment and survive as parasites on human, animal, or plant hosts. Plant-parasitic nematodes can devastate agricultural crops by interfering with roots; the annual economic loss from such pests is estimated at more than $100 billion.

Example: Cuscuta is a stem parasite that naturally grafts to its host plants to extract water and nutrients.

Parasitism in Insects 

Parasitism is a common occurrence in the insect world, and many species of insects are either parasites or hosts to other insects. 


  1. Ichneumonidae wasps: These wasps are parasites of other insects, including caterpillars and pupae. The female wasp lays her eggs on or inside the host, and the larvae feed on the host’s tissues, eventually killing it.
  2. Tachinid flies: Tachinid flies are parasites of other insects, including caterpillars and beetles. The female fly lays her eggs on the host, and the larvae feed on its tissues, eventually killing it.

Do Parasites Harm the Hosts?

Yes. 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.

FAQs on Parasitism

Question 1:How does parasitism affect the environment?


Parasitism has major impacts on host growth unified based on their size, characteristics, interactions with their hosts, and their life cycles.

Question 2: Can parasites survive without a host?


Without a host, a parasite cannot live, grow, and multiply. For this reason, a parasite rarely kills its host, but it can spread diseases, some of which may be fatal.

Question 3: Can parasites change DNA?


Yes, parasites can change the DNA of their hosts. This can happen in several ways:

  • Insertion of parasite DNA: Some parasites, such as viruses, can insert their genetic material into the DNA of their host cells. This can alter the host’s genetic makeup and potentially lead to the development of new traits or diseases.
  • Epigenetic changes: Parasites can also modify the way the host’s DNA is expressed, without changing the DNA itself. For example, some parasites can modify the chemical modifications on the host’s DNA that control gene expression, leading to changes in the host’s phenotype.

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Last Updated : 15 Feb, 2023
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