Science

Real-Life Body Snatchers: Parasites that Manipulate Animal Behavior

Parasites are not the stuff of science fiction; they are real organisms that infest a wide range of creatures, from rats and crickets to ants and moths. These parasites have evolved sophisticated strategies to manipulate the behavior of their hosts, often in the creepiest and most fascinating ways.

Parasites that Alter Host Appearance and Behavior

Some parasites alter the appearance of their hosts to make them more attractive to predators, or to make them less likely to be detected. For example, the parasitic protozoan Toxoplasma gondii, which reproduces inside the gut of cats, makes rats lose their fear of cat urine. In fact, they become sexually attracted to the scent, making them easy prey for felines.

Parasites that Hijack Host Nervous Systems

Other parasites hijack the nervous systems of their hosts, forcing them to behave in ways that benefit the parasite. The hairworm Paragordius tricuspidatus, for example, infects crickets and produces proteins that make them attracted to bright light. This leads the crickets to dive into water, where the hairworm can find a mate and reproduce.

Parasites that Replace Host Organs

In a truly remarkable case of parasitism, the crustacean Cymothoa exigua invades the mouths of snapper fish and replaces their tongues. The parasite hooks itself onto the base of the fish’s tongue and sucks its blood, causing the tongue to atrophy. As the parasite grows, it becomes a functional replacement for the tongue, allowing the fish to continue eating.

Parasitic Wasps and Their Host Control Mechanisms

Parasitic wasps have evolved a wide range of strategies to manipulate their hosts. Some wasps lay their eggs inside the bodies of caterpillars, where the larvae develop and feed on the host’s tissues. As they grow, the larvae release chemicals that alter the caterpillar’s behavior, making it protect the cocoon that the larvae spin.

Other wasps paralyze their hosts and lay their eggs on their bodies. The larvae that hatch from these eggs feed on the host’s blood and eventually kill it. Before dying, the host spider weaves a web that is unlike anything it would normally make, providing a safe environment for the wasp larvae to develop.

Barnacles that Sterilize and Convert Crabs into Surrogate Mothers

The parasitic barnacle Sacculina carcini invades crabs and turns them into surrogate mothers. The barnacle attaches itself to a joint in the crab’s exoskeleton and sends tendrils into the crab’s body, where it steals nutrients from the crab’s blood. The barnacle also releases chemicals that sterilize the crab and make it care for the barnacle’s eggs as if they were its own.

Thorny-Headed Worms that Drive Crustaceans into the Light

The thorny-headed worm Polymorphus paradoxus infects crustaceans and makes them attracted to light. This behavior is beneficial to the worm because it increases the chances that the crustacean will be eaten by a duck, which is the worm’s next host.

Parasitic Maggots that Transform Ladybugs into Guardians

The parasitic wasp Dinocampus coccinellae lays its eggs inside the bodies of ladybugs. The wasp larvae hatch and feed on the ladybug’s tissues. As they grow, they release venoms that alter the ladybug’s behavior, making it guard the cocoon that the larvae spin. After the adult wasp emerges from the cocoon, the ladybug often recovers from the trauma, but the wasp’s fertility is reduced.

Lancet Flukes and Their Multi-Host Life Cycle

Lancet flukes are parasites that have a complex life cycle involving three different hosts: a snail, an ant, and a cow. The fluke eggs are eaten by a snail, which produces slime to trap the larvae. The larvae eventually escape from the snail and are eaten by an ant. Inside the ant, the larvae develop and migrate to the ant’s head and mandibles. They then manipulate the ant’s behavior, making it climb to the top of a blade of grass and bite down. This makes it more likely that the ant will be eaten by a cow, which is the fluke’s final host.

Parasitic Flatworms that Disguise Snails as Caterpillars

The parasitic flatworm Leucochloridium paradoxum infects snails and makes their eyestalks look like juicy caterpillars. This attracts birds, which eat the snails and become infected with the flatworm. Inside the bird, the flatworm reproduces and produces eggs that are passed in the bird’s droppings.

Conclusion

Parasites are fascinating and often terrifying creatures that have evolved a wide range of strategies to manipulate the behavior of their hosts. These parasites play an important role in the ecology of many different ecosystems, and their complex life cycles are a testament to the amazing diversity of life on Earth.