Cleaners are tiny fish living in coral reefs. They regularly clean parasites from much larger fish. Even large predatory fish queue up to be cleaned of skin parasites. The cleaner fish (or sometimes a shrimp) even swims into the predator’s mouth and gills without being eaten.
Birds can do a similar job. A basking crocodile opens its jaws so small birds can pick pieces of food and parasites from between its teeth. Small birds ride on the backs of grazing animals on the African grasslands, picking out skin parasites and feeding on insects as the animal feeds. At the same time the birds act as an early warning system for the host animal, by flying away when danger is near.
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