Ophiocordyceps fungus growing on moth
From Toxoplasma gondii to cordyceps fungi, nature is rife with bizarre and disturbing parasites. It might be best to save this one for when everyone is done eating, because these things are gross. These fungi, worms, protozoans, and other parasites can destroy their hosts' bodies and sometimes even control their minds. But unlike the fleas on your brother's girlfriend's dog (which she kind enough to share with everyone by bringing Fluffy over for dinner) we don't have to worry about most of these parasites bothering us. Andreas Kay via Flickr

If you look closely at nature, you’ll find it’s often too bizarre to believe. Sometimes it doesn’t seem to follow physical laws, but the script of a horror flick written by an overly-imaginative kid. Zombies, abominations, body-snatchers—they’re all real. Nature is full of monsters, but that’s also why it’s awesome. In honor of Halloween, here are six horrific highlights from the animal kingdom.

*Dinocampus coccinellae*

Ladybug Picnic

There is something particularly brutal about an adorable ladybug getting zombified. The perp in this case is a green-eyed wasp known as Dinocampus coccinellae. A female lands on a ladybug and jabs it in the belly, injecting an egg and virus. The egg hatches in situ and the larva goes to work eating the beetle’s insides. It doesn’t kill the beetle though—that’s too kind. Instead, when the larva is big enough, it gnaws its way out of the beetle’s underbelly and starts spinning a cocoon in between its legs. With the virus scrambling up its brain, the ladybug becomes a zombie bodyguard, paralyzed in place over the cocoon. Eventually, an adult wasp emerges, ready to take on life, while the ladybug is left as a dead shell.
*Sacculina carcini*

Ball Buster

Sacculina carcini is a parasitic castrator. Yes, castrator. In its larval stage, it swims freely in the ocean. When it finds a crab, however, it burrows inside a joint opening in the crustacean’s exoskeleton. Inside, it grows, matures, and takes away the crab’s ability to reproduce (hence “castrator”). Eventually, it flops outside the crab as a yellow sac, hanging precisely where the crab’s eggs normally would. As the imposter develops its own eggs, the disillusioned crab cares for and nurtures them as it would its own, ensuring the parasite spreads to other crabs.
*Hymenoepimecis argyraphaga*

Hacking The Web

On a good day, the orb-weaving spider Plesiometa argyra, a native of Costa Rica, spends its time catching unwitting insects in its web and happily sucking them dry. On the worst day of its life, it gets stung by the parasitoid wasp Hymenoepimecis argyraphaga. The attacker paralyzes the unfortunate spider with venom and glues an egg to its back. The freshly hatched larva then gets to feed unmolested upon the living spider—but that’s not the end of it. Like forcing a prisoner to knot his own noose, the larva chemically induces the spider to tear down its web and spin a deformed one instead. The larva spins a cocoon and hangs, safe from danger, in the new web. Meanwhile the spider’s husk, finally drained by the larva, is left to rot.
*Toxoplasma gondii*

Curiosity Killed The Rat

Toxoplasma gondii is a protozoan that can infect nearly any warm blooded mammal, including humans. But it can only sexually reproduce in cats’ bellies. It’s harmless to them…less so to others. When T. gondii winds up in other mammals (it travels around via cat poop), it replicates asexually and embeds itself into organs—even the brain—as little cysts. Still, it always wants to get back to a cat. So in animals like mice and rats—cat lunch and dinner, respectively—the protozoan fiddles with its host’s brain, altering its behavior in ways that make it fearless and even attracted to felines. This, of course, leads to a dead rat and a happy T. gondii back home inside a kitty. Because you were wondering: T. Gondii is prevalent in humans, but is kept in check by a healthy immune system. Pregnant women and people with weak immune systems, however, can develop toxoplasmosis, a serious and sometimes fatal illness. Some studies have suggested that the parasite could also affect behavior and personality in people, but this is still pretty contested.
*Ophiocordyceps fungus*

Dead Ant Walking

If ants could speak, they would probably refer to Ophiocordyceps with abject fear. Small spores of the fungus enter an ant’s body by dissolving its cuticle (skin) with enzymes. Once inside, the fungus grows, filling the ant like a sausage. As it does, it also changes the ant’s brain chemistry and compels it to scale a tree. In its last dying moments, the swollen insect clamps its jaws down on a leaf. With the zombie’s corpse securely anchored, fungal stalks burst from the body and sprinkle spores onto unsuspecting insects below. If a zombie apocalypse ever happens, this has to be how it’s going down.
*Ribeiroia ondatrae*

It’s Not Easy Being Green

In the mid-1990s, federal and state agencies freaked out when kids in the Midwest started finding deformed frogs with extra legs. The culprit turned out to be a trematode, or flatworm, called Ribeiroia ondatrae. The worm begins its journey of destruction in freshwater snails. It produces thousands of clones that eat away a third of the snail’s body—while keeping it alive so it will function as a mobile parasite factory. Then, free-swimming worms pump out of the snail, find a tadpole, and burn their way into its body with acid. They burrow specifically where the tadpole’s back legs will grow, so as it becomes a frog, its limbs morph into twisted, useless appendages. The resulting abominations can barely move around, let alone escape predators, and are easily snatched up by herons. The big birds then carry Ribeiroia hundreds of miles, pooping it out in lakes and ponds as they fly, and perpetuating the grotesque cycle of death.