A parasite is an animal or plant that does not obtain food in the normal way but which lives within or upon another plant or animal (the host) and takes food from it.

Many mammals and birds, for example, have fleas and lice living amongst their fur or feathers and feeding on their blood.

Sometimes you will see threads of a light pinkish plant, known as dodder, entwined amongst the stems of plants such as heather. Dodder contains no green chlorophyll and so is not able to photosynthesise.  It takes its food through suckers that penetrate the stem of its host.

Mistletoe is an example of a partial parasite; it contains chlorophyll but also requires food from another plant. An apple tree is often the host.

The cuckoo is sometimes called a parasite as it lays its eggs in the nests of other birds instead of rearing its own young.

Where a parasite uses a plant or animal of importance to man as its host it may be a serious pest. Liver-flukes are little animals that live inside sheep and can make them ill. Sometimes wheat crops are spoilt by 'rust', a fungus that lives on the ears of wheat.

There are some plants that live on the decaying remains of other plants and animals: such plants are called saprophytes. Like parasitic plants, saprophytes are not able to carry out photosynthesis and do not contain green chlorophyll.

In autumn many fungi grow in woodlands and meadows; they obtain their food from dead leaves and other decaying material in the soil. The field mushroom is an example. Some fungi (moulds, toadstools, etc.) grow on dead timber, others live on dung or animal carcasses. The moulds that grow on stale bread and old cheese are also saprophytic fungi.

A few flowering plants such as the bird's nest orchis are also saprophytes.