Scientists Say: Parasite | Science News for Students

Scientists Say: Parasite

These organisms benefit while their hosts suffer
Oct 29, 2018 — 9:31 am EST
tapeworm gut

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, “PEAR-ah-sight”)

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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Power Words

(more about Power Words)

ectoparasite     A parasite such as a flea or louse, which lives outside of its host.  

egg     The unfertilized reproductive cell made by females.

endoparasite   A parasite such as a tapeworm which lives inside of its host.

gull     A family of long-winged and relatively thick-bodied shoreline birds. Most are gray and white with webbed feet. They tend to be very vocal.

hookworm     A type of bloodsucking nematode (small worm) that lives within the intestines of people and other animals. With hooklike mouthparts, it attaches to the wall of the gut. This parasite punctures blood vessels there to reach the blood it seeks.  

host      (in biology and medicine) The organism (or environment) in which some other thing resides. Humans may be a temporary host for food-poisoning germs or other infective agents.

lice     (in human health) A type of tiny wingless crawling insect that infests hair on the head and neck (although it can be found on eyebrows and eyelashes). This parasite spends its life on the body, feeding on blood through the scalp several times a day. A telltale sign of head lice is the presence of their nits, small white eggs that have been attached at the bottom of hair shafts. Singular form: louse.

organism     Any living thing, from elephants and plants to bacteria and other types of single-celled life.

parasite     An organism that gets benefits from another species, called a host, but doesn’t provide that host any benefits. Classic examples of parasites include ticks, fleas and tapeworms.

pup     A term given to the young of many animals, from dogs and mice to seals.