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Find out more about parasites and their relationship with their host.

Types of parasites

Parasites are plants or animals that live in or on another living thing, getting their food from it while it is still alive. The organisms that they live on are called hosts. Hosts never benefit from parasites. In fact, some parasites eventually cause their hosts to die. 


Tapeworms live in the guts of mammals. Yuk! They need two hosts to complete their life cycle. The first one, such as a mouse, eats their eggs by mistake. The larvae hatch inside its body and live there, until another animal – such as a weasel – eats the mouse. This weasel now becomes the second host. Inside its body the larvae grow into new tapeworms. The weasel will usually survive with a tapeworm inside it, but may be weaker.

Nest mites

Many parasitic animals, such as fleas, ticks and lice, feed on the blood of larger animals. By attaching themselves to their host, they get a ready meal wherever it goes. Some birds are crawling with this kind of parasite. Nest mites lurk in nests where they suck the blood of the nestlings. When the young birds are ready to fly, the mites hop on board and hitch a ride to a new host. More than 5,000 nest mites have been found in one house martin’s nest!


Even some plants are parasitic. They don’t make all their own food, like other plants do. Mistletoe has no roots of its own, so it can’t get nutrients from the soil. Instead it grows on other trees, and sucks food and water directly from their trunk. But unlike some parasitic plants, mistletoe is still green so makes food by photosynthesis.