When you hear 'zombie', the first thing that probably flashes through your mind is the TV show The Walking Dead. But instead of turning into a zombie because you got bit by a Walker, scientists reckon you could be a walking zombie, right this moment.
Especially if you own a cat.
Researchers claim that a parasite found in cat poop can pass into our central nervous system and cause behavioural changes in humans, e.g. trigger schizophrenia. Toxoplasma gondii infects us and cats. It is also the parasite that causes mice to be attracted to cat urine.
Quite a complex life cycle, but it's only one of many in nature. The rabies virus has a similar 'zombifiying' effect on humans. When it attacks the nervous system, it causes humans to develop an irrational fear of water.
Despite how they make us feel, parasites are essential for maintaining the balance of the ecosystem. They outnumber animals and plants by millions to one, and have evolved clever ways to maintain those numbers.
One example is Cymothoa exigua, the tongue-eating louse. This parasite enters its fish host through its gills and heads up to the mouth. Once there, the louse clamps onto the tongue, causing it to eventually atrophy and fall off. The louse moves into place and becomes the new 'fish tongue'. It continues to feed off the host's blood until the fish dies, before it finally detaches itself.
While you ponder that, here are 10 even nastier parasites you may wanna learn about.
10 Chordodes “Castrate Him” formosanus
The praying mantis is a predator in its own right, feared by many insects and small animals. But even its speed and spiked forelimbs are no match for C. formosanu, a parasite, also known as a hairworm, horsehair worm, or Gordian worm. It starts life as a larva in the gut of the small insects that the mantis preys on. Once ingested by the mantis, C. formosanus starts to grow.
When it's mature, the worm secretes proteins that take over the host's nervous system. It directs the mantis to a body of water and causes it to jump in so that the worm can be excreted. These worms can grow up to 90cm long. For this to occur inside the mantis, the worm must consume its internal organs. By the time the worm leaves, the mantis is just an empty shell. In the male mantis, the worm also causes the testes to shrink and shrivel up.
So the hairworm basically castrates the male mantis, disembowels it, then eventually drowns it in a pond.
9 Kudoa "Liquefy Her" Islandica
The Atlantic wolffish and its cousin the Spotted wolffish won't win any beauty prizes, but what they lack in looks, they make up for in flavour. They're a delicacy in Iceland and their skin can be fashioned into a type of designer leather.
However, these fish have an even bigger problem than man and his belly. In the wild, they are prone to infection by K. islandica. This is a myxosporean parasite that lives in both fresh and marine habitats. Samples of fish caught are so loaded with the parasite that they have replaced portions of the fish flesh. The fish don't seem to suffer any side-effects from the 'flesh replacement', but when they die and the pH in the body changes, things get a little messy.
K. islandica liquefies the internal organs of the fish, so that the parasite larva can leave the host and pass on to another. Since the parasite isn't picky about which fish it infects, there is a huge potential of mass infection of other fish species in Iceland.
8 Polysphincta “Wrap Me Tight” boops
Like many spiders, orb-weavers spin intricate webs to trap small bugs to feed on. P. boops is a parasitoid wasp that likes to return the favor. This parasite sneaks up on the spider and knocks it out with a sting; with the spider unconscious, the wasp injects an egg into its abdomen. When the spider awakens a few hours later, it is none the wiser.
When the egg hatches, the larva develops by feeding off the spider's blood. After a few weeks, the larva starts secreting neurotransmitters that alter the spider's normal behavior. Instead of spinning orb-shaped webs to trap food, the spider spins a web that is denser in the middle and can withstand adverse weather.
With the web done, the larva kills the host by eating its internal organs. It emerges into the cocoon built to provide protection for it in its final growth stages.
7 Ophiocordyceps “Zombie Fungus” unilateralis
Despite the social nature of the ant, researchers have found one organism that can change their 'normal routine'. When a spore of the fungus O. unilateralis comes in contact with an ant, it enters the body through microscopic holes in its exoskeleton. The fungus starts to grow inside of the insect, consuming all but the most vital organs. It spares those as it needs them to keep the ant alive and functional.
When the fungus is ready to release spores for reproduction, it produces toxins that take over the ant's brain. The ant is then 'led' out of the colony and up to the highest point of any nearby plant. Up there, it crawls under a leaf and holds on with its mandibles. Once the ant has latched on, the fungus dissolves the muscles which control those mandibles, leaving the ant dangling up to 15 inches off the ground.
Within three weeks, the top of the ant's head splits open as the fungus produces a 'stalk' packed with spores. When these spores are sexually mature, the capsule explodes, releasing spores into the path of healthy ants, and the cycle starts again.
Fun Fact: Ophiocordyceps unilateralis was the inspiration for the fungus zombies in the game The Last of Us.
6 Wolbachia “The Male Massacring” species
This bacteria infects between 25% and 70% of ALL insect species, and is considered to be one of Nature's most parasitic microbes. Wolbachia is solely responsible for decimating the population of the male Blue Moon butterfly in the Samoan Islands. Cockroaches, flatworms, wasps, moths, other parasites are not safe from this bacteria, either.
To ensure its survival, this parasite has evolved some really scary tactics; let's look at its impact on the Blue Moon butterfly. Since it lives inside the female butterfly’s reproductive cells, the bacteria has little or no use for male butterflies. Therefore, it has developed ways to eliminate the 'useless' males.
Wolbachia sp. either kills off the male embryo, feminizes the males, or causes the females to procreate without needing a male! In a cruel twist of nature, some insect species have become so dependent on this bacteria that they can't reproduce or even survive without it.
5 Dicroelium “Slimy Customer” dentriticum
Like T. gondii, D. dentriticum uses many avenues to complete its life cycle. It infects snails, ants and grazing animals like sheep and cattle. When snails eat grass that has been contaminated with infected cow poo, they ingest unborn lancet flukes.
In the snail's belly, the fluke eggs are released from their shells by its digestive juices. The parasites grow in its digestive gland and when mature, move towards the respiratory chamber. Their presence here irritates the snail, and it coughs them out, coated in thick mucus. Protected by 'snail phlegm', these parasites wait to be picked up again.
Attracted by the pheromones in the snail 'hairball', ants pick them up and take them to their colony. Upon consumption of said hairball, the parasites make their way into the ant's brain to settle in.
The parasite interrupts normal ant behavior, causing it to go out in the evening, climb a tall leaf and wait to be eaten by a cow, thus starting the cycle all over again. Like O. unilateralis, this parasite zombifies an ant, causing it to abandon its colony and basically commit suicide.
4 Leucochloridium “Disco Dancer” paradoxum
L. paradoxum is a parasitic worm that invades a snail's eyestalks. While it doesn't cause the snail to go blind, what it does is much worse. The life cycle starts when the snail ingests the worm's egg which grows into a sporocyst in its liver.
The sporocyst survives by absorbing essential nutrients from its host. To ensure it gets as much as possible, the greedy parasite also castrates the snail. After gorging itself, it sends tentacles from the liver to the snail's eyestalks, where it forms a broodsac full of larvae. These start to pulse, causing the eyestalks to swell up to three times their normal size.
Seen from above, the bands of pulsing color make the eyestalk look like a plump caterpillar, making them (and them alone) a prime target for birds looking for a meal. Once ingested by a bird, the worm reproduces and its spores are passed out with bird poo. Droppings are consumed by snails and the freaky cycle continues.
3 Pseudacteon “Queen of Hearts” litoralis
Fire ants are known for their painful bites, so most species tend to avoid them. If ants could avoid P. litoralis, I bet they would. Members of the genus, Pseudacteon, seek out fire ants by pheromone and proceed to 'hand off' their young.
Upon finding an ant, the female fly spears it with a razor sharp ovipositor to deposit an egg directly into the ant's gut. Within a few days, the egg grows and hatches into a maggot which makes its way to the ant's head. It spends a few weeks here feeding and getting bigger. The maggot ensures the ant keeps up appearances, as it's important that it stays with the colony, where food is plentiful.
But 24 hours before the maggot is ready to pupate, it directs the ant away from the colony and into the humid floor of the forest. Once there, it secretes chemicals that dissolve membranes in the body, including the one that holds the head in place. The head soon falls off, but the larva sticks around for 12 days, eating the remaining muscles and brain while developing into an adult fly.
2 Asobara “Playing God” japonica
A. japonica is a hyperparasite i.e. a parasite that parasites on other parasites. Crazy, I know. Its host is Drosophila suzukii, a fruit fly that lays eggs in ripening fruits. This makes D. suzukii a serious pest, as it attacks a wide range of soft-skinned fruits e.g. cherries, grapes, strawberries etc.
Like P. litoralis, it injects the host with eggs but it also injects a potent venom that almost kills it. The venom induces paralysis in the host, thereby preventing it from protecting itself from the parasite eggs. The wasp doesn't allow the venom kill the fly as it also injects it with an antidote that allows it continue to function, albeit without an immune system.
This allows the eggs and larva of the wasp to grow in a safe, nutritious environment, like a living incubator.
1 Sacculina “The Body Snatcher” carcini
You probably associate barnacles with ships, and boats. You'd never think of a barnacle as a parasite, right? Then thank your stars that you're not a crab, and never have to face Sacculina carcini.
S. carcini 'barnacles' start life as free-swimming larva, until they find a suitable crab host.Then the story quickly becomes ugly. First, the microscopic female larva finds a chink in the crab armor and injects itself into the underside of the crab. This infection quickly grows into a visible bulge and the parasite sends its tendrils into the host, to draw nutrients. As she grows in size, she also destroys the host's genitalia. A male Sacculina soon arrives to implant himself inside the female INSIDE the host crab.
As they reproduce and lay their eggs, the crab becomes a zombie nanny. It stops feeding itself and growing; it now exists only to take care of the barnacle's eggs. Sacculina doesn't attack only female crabs; it does the same to males, and in even weirder ways.
It secretes neurotransmitters that make the male host become more feminine. To accommodate its eggs, this parasite cause structural changes like widening and flattening of the abdomen in male crabs.
Plus, it castrates males crabs too.