Charles and Fanny Brewer-Carias
Once a parasite has used up its host, it needs to escape. A fungus emerges from an ant.
Andreas Schmidt-Rhaesa
A worm-like parasite called a nematomorph escapes its cricket host.
Thomas Dunagan
Thorny-headed worms, like many parasites, live in two or more hosts during their life. Many of them live initially in insects or crustaceans and then move into predators such as birds. To get into these predators, the parasites make their intermediate hosts stupid and foolhardy—and thus easily preyed upon.
Jens Hoeg
Top: The parasitic barnacle Sacculina carcini invades crabs and fills up their entire body with a network of roots. It forms a sac full of larvae where the crab’s own egg pouch should be (middle), and it forces the crab to care for its young.
Todd Huspeni, University of California, Santa Barbara
Todd Huspeni, University of California, Santa Barbara
Bottom: Snails can also be horrifically victimized when they are infected with the fluke Leucochloridium paradoxum. The parasite’s final hosts are birds. To get their attention, the parasite climbs into the snail’s transparent tentacles. The striped flukes, which can be seen through the tentacles, look like caterpillars, and they catch the eye of hungry birds.
David Kjaer/BBCWild
Cuckoos are a special sort of parasite—they don’t live inside other animals, but they steal parental care. They lay their eggs in the nests of other bird species and trick the foster parents into rearing them. Here a reed warbler contemplates the giant cuckoo nestling that has taken its own offspring’s place.
Only a few parasites of humans are on the verge of eradication. For centuries people have extracted guinea worms from their legs by gently spooling them onto sticks. Public health campaigns have driven down guinea worms to less than 100,000 cases a year and are on the verge of eradicating the parasite altogether.
In 1998 a new campaign was launched to wipe out elephantiasis, caused by microscopic worms that block lymph nodes.
AFIP NEG. NO. 68-2740
Parasites sometimes make mistakes, and the results can be lethal. Normally, tapeworms first mature in a cyst in intermediate hosts such as cows or pigs before they move on to humans. But if their eggs should end up in a human body, they will go ahead and form a cyst anyway, often in the brain.
AFIP NEG. NO. N-50807
A botfly laid its eggs on a penetrated his brain.
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Photo by Michael A. Huffman
Hosts have had to evolve ways to fend off the ever-present threat of parasites. Chimpanzees eat medicinal plants to fight off invaders.
Fox/Everett Collection
Hollywood has a healthy respect for the sophistication and cunning of parasites. In the television show The X-Files, a fungus attacks people in the same way that some real fungi attack insects.
Everett Collection
In the Alien movie series, a creature fashioned after parasitic wasps plants its young in the chests of human hosts.