African oxpeckers
African oxpeckers (Buphagus africanus and Buphagus erythrorhynchus) feed on the backs of zebra, elephants, hippopotamuses and other large African animals. Once thought to be friendly tick-eating helpers, they’re actually vampire birds, sucking blood out of open tick-wounds. This shows how the line between symbiotic assistant and parasite can be blurred. Oxpeckers do eat ticks as well, and some animals may be happy to sacrifice a bit of blood for this service. Oxpeckers may also be tolerated because they produce a hissing scream when startled – like a personal danger alarm.