Scientists Say: Parasite

These organisms benefit while their hosts suffer


This is a tapeworm in a person’s gut. It’s attached itself to the gut wall and will feed off the food the person eats — making it a parasite.


Parasite (noun, “PAIR-ah-syt”)

This is an organism that lives on or in another organism known as a host. Parasites are terrible guests. A parasite benefits from its host, but the host suffers. The relationship is called parasitism.

Parasites can feed off the food a host eats, bite a host for food or burrow inside a host to lay their eggs. This causes harm to the hosts — they can’t get as much food or suffer from itchy bug bites, for instance, and might become sick.

Parasites that live inside a host — such as hookworms and ringworms — are called endoparasites (“endo” is from Greek and means “inside”). Parasites such as lice and fleas that live outside a host are called ectoparasites (“ecto” is also Greek and means “outside”).

In a sentence

Parasites living inside a seal pup’s poop are so delicious that gulls will bite the babies in the butt to get at them.

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Bethany Brookshire was a longtime staff writer at Science News Explores and is the author of the book Pests: How Humans Create Animal Villains. She has a Ph.D. in physiology and pharmacology and likes to write about neuroscience, biology, climate and more. She thinks Porgs are an invasive species.

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