Scientists Say: Ectoparasite

This is parasite that lives on — not in — another organism


This is a human head louse. It’s a type of parasite that can live on a person’s scalp.

Giles San Martin/Wikimedia Commons (CC BY-SA 2.0)

Ectoparasite (noun, “ECK-to-PAIR-a-site”)

Like a terrible houseguest, a parasite relies on another organism — one it lives on or in — for its nutrients and gives nothing in return. The parasite benefits, while the host usually suffers in some way. Many parasites, such as tapeworms, live inside the host’s body. But ectoparasites are found outside the host. (“Ecto-“ is from the Greek language, and means “outside.”) Examples include a dog’s fleas and the head lice that spread from kid to kid in the classroom.

In a sentence

Lice and fleas that lived on people were ectoparasites that helped spread the infamous Black Death through Europe.

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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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