Parasitism: Examples & Definition

Lesson Transcript
Laura Enzor

Laura has a Master's degree in Biology and is working on her PhD in Biology. She specializes in teaching Human Physiology at USC.

Expert Contributor
Amanda Robb

Amanda has taught high school science for over 10 years. They have a Master's Degree in Cellular and Molecular Physiology from Tufts Medical School and a Master's of Teaching from Simmons College. They also are certified in secondary special education, biology, and physics in Massachusetts.

When two organisms have a relationship where one benefits and the other is harmed, it is called parasitism. Examine the types of parasitism, special cases, examples, and defenses against parasitism. Updated: 09/06/2021


Parasitism describes a relationship between two organisms where one benefits, and the other is harmed. The parasite is the organism that benefits from the relationship, while the host is harmed by the relationship. Parasites can be a number of things including plants, animals and even viruses and bacteria.

It is useful to know about parasitism because, technically, anything that is benefited while we are harmed is considered a parasite. Yes, that pesky mosquito that keeps biting you just gained an official title. While some of the parasites that affect humans can be a nuisance, such as lice or bedbugs, there are other parasites that can make us really sick, such as a bite from a tick, which can cause Lyme disease, or giardia, which we ingest by drinking contaminated water.

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  • 0:00 Parasitism
  • 0:56 Types
  • 1:56 Special Cases
  • 3:27 Defenses
  • 3:53 Lesson Summary
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Parasites are classified by how they interact with their host. Overall, parasites are much smaller than their hosts and reproduce at a faster rate.

Parasites that live on their host are termed ectoparasites. Examples of ectoparasites are fleas, ticks and mites. These parasites live on larger animals, like cats, dogs and deer. Parasites that live inside their host are termed endoparasites. These include things like parasitic worms, bacteria and viruses. One interesting case of an endoparasite is the hornworm caterpillar and the braconid wasp. The wasp lays eggs inside the hornworm, which then hatch and kill the host. This relationship is considered beneficial to humans, because hornworms eat the leaves on plants, such as tomatoes, eggplants and potatoes, and ruin a lot of crops for farmers.

Ectoparasitism and Endoparasitism

Special Cases

An epiparasite is a parasite that feeds on another parasite. A common example of this is a protozoan that lives in the digestive tract of a flea, which then parasitizes a dog or cat.

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Additional Activities

Parasite Diseases

In this activity, students will be researching different diseases caused by parasites. Students are generally very interested in this topic and their research will expand on the information presented in the lesson.

Tips and Examples:

If students are having trouble thinking of a parasite born disease, have them start with a basic internet search for human parasites. Make sure that students are using quality sources, such as Mayo Clinic, National Health Service, WebMD, or other sources from a news outlet, a scientist, or the government. Some examples of parasitic infections that students might research include malaria, ringworm, or tapeworms.

Student Directions

Now that you've read about the different types of parasites, you're going to research one in depth that causes an infection in humans. For your final product, you can create a slide show online, a poster, a pamphlet, or write an essay of at least 1,000 words. However, whichever product you choose should have the following information:

  • Name of the parasite and the infection it causes
  • How the parasite is contracted
  • Symptoms of the infection
  • How the infection is diagnosed
  • Treatment and prevention
  • Risk factors for infection
  • The type of parasite it is: ectoparasite, endoparasite, epiparasite, social parasite, or a brood parasite

Make sure your information comes from reliable sources. If possible, you should cross-check your information by finding it from at least two different reliable sources. Include the source(s) of your information at the end of your project.

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