What is a Parasite?


Renotkil TechnicianThe term parasite comes from parasitism. Parasitism refers to “the relationship between two species, where one species, the parasite, benefits at the expense of another, the host.” – Encyclopadeia Britannica

Types of Parasite

Parasites come in all shapes and sizes. Each of them have their own characteristics that affect the host in their own unique way. However parasites can be separated into two groups based on both their interactions with their hosts and how it affects their life cycles.

Obligate Parasite

An obligate parasite refers to an organism that cannot complete its life cycle without exploiting a suitable host. If an obligate parasite cannot connect to a host subject, then it will fail to reproduce. Obligate parasites are come in a range of different organisms from viruses and bacteria to fungi, plants, and animals.

Obligate parasites can sometimes use two hosts in their life time. The first is merely a vessel to reach their desired host. For example some parasites will attach themselves to the prey of their desired host in order to make the transfer.

Facultative Parasite

A facultative parasite is an organism which resorts to parasitic behaviours but does not rely on a host subject to survive and complete its life cycle. Facultative parasites are normally micro organisms and vegetation, with little to no insect parasites existing in this category.

Among both these categories two different types of parasites exist:

  • Ectoparasites – Ectoparasites are parasites who live on the outside of their host. These include insects such as fleas.
  • EndoparasitesEndoparasites are parasites who live inside their host. Endoparasites can exist within two forms:
    • Intercellular parasites – Parasites which inhabit space within the host’s body.
    • Intracellular parasites – Parasites which inhabit cells within the host’s body.

Insect Parasites

In regards to pest control and parasites, the majority of organisms found within this category are those from the insect world.

Common Parasites

Bed BugsBed Bugs

Bed bugs are one of the main parasites which affect humans due to their vampiric nature.

  • Bed bugs are Ectoparasites – They live near on the outside of their host on mattresses and cracks in the floor and walls.
  • They rely on human blood to complete their life cycle making them Obligate parasites.
  • Quite small in size but can be seen by the human eye.
  • Bed Bugs will often travel through luggage and second hand furniture in order to find a suitable host.


Fleas are another common parasite within the pest world which are a regular source of nuisance irritating us and our pets.

  • Fleas are external parasites (Ectoparasites) living on the outside of their hosts. Usually found on the fur of household pets such as cats and dogs.
  • Like bed bugs they are obligate parasites, living off the blood of their hosts.
  • Fleas are wingless insects but are agile and quick.
  • With a suitable food source an adult flea can live up to 100 days.

Other Parasites

One parasite that is important to mention is plasmodium. Although not an actual pest, its involvement with a common pest makes it worth noting.


More commonly known as the malaria parasite, plasmodium is the microorganism which causes malaria within humans.

  • Plasmodium is an obligate parasite.
  • It is an intracellular parasite living inside the cells of its host.
  • Plasmodium uses two hosts in a lifetime. It first affects the mosquito in order to find its desired host, a human. It then transfers itself through the saliva of the female insect when the pest is feeding on a human.

The world is full of parasites, some of which are considered a pest due to their conflict with man.

Do you have a bed bug or flea infestation in your household and/or workplace? Contact your local Rentokil business for a free quote.


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