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Nature's Puppet Masters

From Christmas cheer to... parasites. If you thought our article on fig wasps was disturbing, get ready... Mother Nature has some other horrifying tricks up her sleeve, like parasites that can alter the DNA of their host, affecting not only their brains but their behavior.


By definition, a parasite is a plant or animal organism that lives in or on a host organism, and gets its food from or at the expense of its host. A parasitic relationship, or parasitism, is the relationship between two species of plants or animals in which one party benefits at the expense of the other. In most cases this results in the death of the host, but not always.


First up, nature’s ultimate Type-A planner: toxoplasma gondii. This parasite can only sexually reproduce inside a cat’s intestines (talk about setting the mood). In order to maximize its chances of entering the feline gut, the toxoplasma parasite has made some impressive adaptations. To make its way into a cat’s gut the toxoplasma parasite must first infect a different host - most typically rodents. Once safely inside a rodent, the parasite alters the host's brain chemistry in such a way that causes it to lose its fear of a cat’s odor. As a result, the rodent (who typically avoids approaching cats) now stays put, as it no longer fears the predator’s scent - making it easy prey for curious felines. In this manner, the toxoplasma is consumed alongside the rodent and can safely begin getting it on inside the cat’s intestines.


Another example is the Gordian worm, more commonly referred to as the Horsehair worm due to its long and stringy appearance. Over 350 species of this parasite are known to exist. The horsehair worm infects its host and then remains dormant over the course of several months while it develops and grows. A common host is the cricket, where the horsehair worm can grow up to a foot long inside the insect. Once developed, the mind-control begins. The horsehair worm produces neurotransmitters that alter the crickets brain activity and causes it to stop chirping, making it less likely to be the target of its numerous predators. Once the horsehair is ready to reproduce, it will again alter the host’s mind to make it believe it is an Olympic-level swimmer. Crickets normally shy away from running water as that tends to be where its predators live. However, a cricket infected with a horsehair worm will think it's the next Michael Phelps and not only get close to water, but eventually take a nose-dive directly into the depths! Once submerged, the horsehair worm bores its way through the cricket’s exoskeleton to make its escape, search for a mate, and lay its larvae - who begin the process all over again.


Deadly, sure, but parasites play a prominent role in biodiversity and the food chain. These relationships are paramount in nature to keep things in regulation. Without them, entire ecosystems would be in jeopardy, causing populations to grow unregulated. They're so vital that an international group of scientists have begun plans for a parasite conservation project to preserve and protect them, as their responses to environmental change could lead to the loss of certain species.


Learn more:

Parasite makes mice lose fear of cats permanently

Britannica: Parasitism

The Parasitic Worm That Turns Crickets into Suicidal Maniacs

New studies show how to save parasites and why it's important

Image by Alastair Rae/flickr/CC BY-SA 2.0

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