7 More Zombie Animals

Last week's post Invasion of the Zombie Animals proved to be "interesting" for many, even those who were grossed out. Further research has yielded even more interesting parasites that take over and change the body, mind, and life of their victims.

1. A Big Red Butt

A parasitic nematode named Myrmeconema neotropicum targets the gliding ant Cephalotes atratus in the Central and South America rain forests on its way to infecting birds. The nematodes travel to the ant's abdomen, and as they mature, cause the abdomen to grow round and bright red! The ants will hold their abdomens, or gasters, high as if to draw attention -which they do. The red gasters look like berries and are eaten by birds who normally don't eat insects. The nematodes then live in the bird's digestive tract.

2. A New Web Design

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Hymenoepimecis argyraphaga is a parasitic wasp found in Costa Rica. It infects one particular spider species, Plesiometa argyra. An adult wasp lays an egg on the spider's abdomen. When it hatches, it attaches itself to the spider and sucks its blood. When the right time comes, it releases a chemical into the spider that causes it to spin a web unlike any it would naturally spin. This web is designed to protect the wasp instead of feeding the spider. When the web is ready, the wasp larvae will kill the spider, eat it, and set up a cocoon in the safety of the web the spider built under the wasp larva's control.

3. Back to the Cat

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Toxoplasma gondii is a protozoa that is normally parasitic to cats, but can survive in other species of mammals or birds, including humans. It causes the disease Toxoplasmosis, which is usually mild or even asymptomatic in humans, but can be dangerous for a fetus or those with compromised immune systems. Toxoplasma gondii affects the behavior of rats in a curious way -it makes them less afraid of, and even friendly to cats! Therefore, a rat with the infection is more likely to be eaten by a cat, which is the preferred victim as T. gondii reproduce inside cats. Does the parasite change human behavior, too?

Some scientists believe that Toxoplasma changes the personality of its human hosts, bringing different shifts to men and women. Parasitologist Jaroslav Flegr of Charles University in Prague administered psychological questionnaires to people infected with Toxoplasma and controls. Those infected, he found, show a small, but statistically significant, tendency to be more self-reproaching and insecure. Paradoxically, infected women, on average, tend to be more outgoing and warmhearted than controls, while infected men tend to be more jealous and suspicious.

How this benefits the parasite is anyone's guess, but it may be chemically linked to the way T. gondii has evolved to get from the rat to the cat.

4. Fire Ant Foe

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The phorid fly (Phoridae) is also called a humpback fly due to its appearance, a scuttling fly due to its tendency to run instead of fly when disturbed, or a decapitating fly due to its habit of feeding on the brains of fire ants. Some species of phorid fly attack and then lay eggs in the body of a fire ant. The eggs hatch, and the larva make its way to the ant's head where it eats it from the inside out. The ant does not immediately die, but will walk around with no direction or purpose once its brains are gone. When the larva matures, it causes the ant's head to fall off so it can emerge as an adult fly.

Fire ants are an invasive non-native species in the US, and phorid flies have been introduced in the south as a method of controlling the fire ant population, most recently in Texas. Phorid flies have been in use in Alabama for fire ant control since 1998. Other species of phorid fly are called coffin flies. They lay eggs in human remains and can survive several generations inside a sealed coffin. Forensic pathologists study phorid fly infestations to determine how long a body has been dead.

5. A Fungus Among Us

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Cordyceps unilateralis infects ants for travel purposes in order to spread its spores. Oh, it eats them, too, but first the fungus will enter the brain and alter the ant's behavior over several days, making it climb to the top of a blade of grass. The ant will bite the grass for a secure hold. Only then will the fungus kill the ant and explode out of the head. The spores are then borne on the wind to parts unknown. See a video of Cordyceps in action.

6. Shrimp and Duck for Dinner

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Thorny-headed worms (Acanthocephala) are 1150 species of parasite with hooks on their probosces (they don't have real mouths). They use these hooks to latch onto a victim. A couple of species target the crustacean Gammarus lacustris, or blue shrimp. Once inside, the worm changes the shrimp's chemistry, possibly affecting serotonin levels. The shrimp loses interest in mating and swims dangerously close to the surface. It will bite onto and cling to plants at the water's surface, which makes it easy prey for hungry ducks. When a ducks eats the shrimp, the thorny-headed worm has found its home. It lays its eggs inside the duck, completing its life cycle.

7. Take Me To The Liver

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Dicroelium dentriticum or Lancet Liver Fluke work in much the same way the thorny-headed worm does, only on different animals. The fluke infects three species in order, snails, ants, and sheep or cattle during its life cycle, but it only controls the behavior of the ant. One the fluke has settled in the ant's nervous system, the ant will go about its regular duties during the heat of the day, but crawl up to the top of a blade of grass in the cool mornings and evenings when it is most likely to be eaten by a sheep or cow. It will then spend its adult life inside the animal's liver.

Special thanks to Carl Zimmer for help on this post.

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May 14, 2009 - 4:36am
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