Parasitism Lesson for Kids: Definition & Examples

Instructor: Jennifer Farrell

Jen has taught Science in accredited schools in North & South America for thirteen years and has a degree in Sociology (Epidemiology & Aids Research).

Parasites are everywhere! They live on our skin, in our food, and in the air. In this lesson, we investigate different types of parasitism and will learn some common examples of each.


They're everywhere and in all shapes and forms. You breathe them in, you eat them, they even live on your body. And who are 'they,' you might ask? Parasites.

If the beginning of this lesson already has you wanting to take an extra-long shower or washing your hands more carefully, I get it. But don't bother because there is no escaping parasites, no matter how clean or stinky you are.

Parasitism is a relationship between two living things. In this kind of relationship, one member benefits (the parasite) and the other member is usually harmed (the host). Parasites are almost always smaller than the host and account for roughly 50% of all species found on Earth.

But just because a parasite is living off a host doesn't automatically mean the host is going to be hurt badly. In fact, parasites NEED the host to stay alive so that they can, too! There are some parasites that can do good things for their host. In the old days, people used to put leeches on injuries like skin diseases or infections because the leech would suck out the bad blood!

Let's look at some different kinds of parasites that may be found on humans.


An ectoparasite lives on the outside of its host and are most commonly known to be blood-sucking.

Head Lice

Head lice lay eggs on a person's eyebrows, eye lashes, and head. They do best in a clean environment. They cannot fly or hop, but can crawl. Head lice are passed from person to person when there is direct contact with the infested person's hair. In other words, when two people's heads touch.


Ticks love to feast on blood. They are commonly associated with living on dogs and cats, but will use humans as hosts, too. Ticks will attach to their host by burying their head into their skin. Their bodies fill up and expand as they drink, most often falling off when they're full.



Did you know that the deadliest animal on Earth is the mosquito? The diseases that some mosquitos can carry and pass on to people by biting them kill several million people around the world every year. Mosquitoes puncture your skin and sip your blood, often times before the host even realizes it.


Endoparasites live on the inside of their host and feed off their digestive system, where all the nutrients from your food travel through.

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