Mother Nature is not usually kind. There are creatures, usually tiny creatures, that will take over a member of another species. They will invade their host's bodies, their brains, and even their will. They turn their much-larger victims into zombies!
1. Zombie Snails -Induced Vulnerability
The flatworm Leucochloridium paradoxum infects two different animals in its lifetime, but only controls one of them. It lives its adult life inside birds and its eggs are spread by bird excretion. How does it get inside the birds? That's the horror story. Amber snails eat the eggs, which hatch in the snail's digestive tract. The larva changes into sporocysts (or broodsacs), which elongate and invade the snail's tentacles atop its head. The broodsacs, filled with hundred of Leucochloridium paradoxum, pulsate and seek light. The snail is helpless to retract its tentacles, and has lost its ability to perceive light and therefore does not hide. The inflated tentacles move like worms, attracting birds that bite off the tentacles. The flatworms then develop into the adult stage inside the bird. The snail, however, is left to die -or to undergo the process again.
2. Zombie Crabs -Slave Governess
A barnacle named Sacculina wants to nest inside a crab. A female Sacculina will look for a place to enter the crab's body. When it does, it will leave its shell behind, not needing it anymore as it has the crab! Inside, Sacculina sets up shop, growing tendrils through the crab's body and slowly feeding on it. It castrates the crab (if male) and effectively turns the crab into a female nanny for its young. This makes the crab not only infertile but also uninterested in mating. The barnacle, on the other hand, bores a hole open in the crab's shell big enough to let male Sacculina in to mate. The zombie crab treats the Sacculina eggs and larvae as its own, having lost the will to do anything but serve its parasite master. Image credit: Hans Hillewaert.
3. Zombie Caterpillars -Slave Bodyguard
Glyptapanteles is a wasp that lays its eggs in the body of a caterpillar. This is a three layered parasitic infection. The wasps engage the help of a virus, or more accurately a polydnavirus that has been genetically modified by the wasps, to disable the caterpillar's immune system, allowing the wasp eggs to survive. The relationship between the wasps and the virus is mutually beneficial; only the caterpillars get the short end of the stick. The eggs hatch and feed on the caterpillar, but do not kill it. Instead, the caterpillar stops developing and spends the rest of its life protecting the wasp larva, even going as far as spinning its own cocoon around the wasp pupae. Watch a video of the entire process. When the adult wasp emerges from its cocoon, the zombie caterpillar finally tastes the sweet release of death.
4. Zombie Grasshoppers -Induced Suicide
The parasitic hairworm Spinochordodes tellinii is deadly to grasshoppers. Once eaten by a grasshopper or cricket, the larval worm produces proteins that affect the insect's brain and nervous system. By the time the worm reaches adulthood, the insect is completely under its power. The zombie grasshopper commits suicide by jumping into water, where the worm will emerge and look for a mate.
5. Zombie Fish -Luring Its Killer
The parasitic worm Euhaplorchis californiensis infects three other species in a cycle, and alters the behavior of two of them. First, the eggs are consumed by horn snails. While living inside a snail, sometimes for several generations, Euhaplorchis inhibits the snail's fertility. The parasite will eventually leave the snail and infect the gills of a killifish. The worms will surround the fish's brain and cause it to swim near the surface and wiggle around. This makes the fish more likely to be eaten by a bird, which is what Euhaplorchis wanted in the first place. The digestive system of a bird is where the worm lays its eggs, which are excreted onto the beach where snails can reach them.
6. Zombie Ants -Serving the Impostors
Even butterflies can make other species into zombies! Maculina rebeli, a European butterfly, lay eggs that exude the scent of ant queens. Worker ants welcome them into their colony. The butterflies emerge as caterpillars which are fed by the ants. The ants treat them as their own young, or even better than ordinary ant larvae since they perceive the caterpillars to be queen ant larvae. Worker ants will even defend the caterpillars against their own queen! You may think of ants as zombies already, but they normally only serve their own species.
7. Zombie Fish Tongue -Artificial Organ
Cymothoa exigua is a small crustacean found off the coast of California. You don't have to worry about it unless you are a spotted rose snapper. C. exigua invades the mouth of these fish and grabs onto the base of the tongue, pinching off the blood supply and drinking it. As the tongue atrophies, the fish begins to use the little isopod as a replacement tongue. Meanwhile, C. exigua lives its life inside the fish's mouth, drinking blood and fish slime from the tongue's stump. Other than the loss of its tongue, the fish suffers little from the experience, so the two can share a normal, if creepy, lifespan.
8. Zombie Cockroach -Commandeered Nursery
The Emerald Cockroach Wasp (Ampulex compressa) makes a slave out a much larger cockroach. The wasp will sting the roach twice, paralyzing its front legs and taking the escape reflex away from its brain. Then the wasp will chew off half of the roach's antennae and uses what's left to steer the roach to a prepared nest. The wasp lays an egg on the roach's abdomen and leaves. The egg will hatch and feed off the roach, which still won't try to escape. The wasp larvae keeps the docile roach alive long enough to build a cocoon inside the roach's body and transform into an adult wasp. An adult female wasp can enslave and lays eggs on several dozen zombie roaches.
Are there organisms that will have effects like this on human behavior? I believe there may be, but the voices in my head tell me they are a secret.
Update: Also see the sequel to this post, 7 More Zombie Animals