You Think You’re So Smart

We are always very happy to construct evolutionary pyramids beginning with the basic single celled life forms at the bottom and culminating with us at the apex, the very peak of intelligence. However, were we to construct a pyramid of cunning and manipulation we would almost certainly be nowhere near the top, while those life forms we consign to the depths of the intelligence pyramid would do very well when it comes to being crafty and underhanded. But then, if you can’t use intelligence to survive, you need to find other ways to make a living. Here are a few of the more wily members of the animal kingdom.

1)      Gordius. This is a large parasitic worm that lives in water. The eggs and/or larvae it produces are inadvertently drunk by a spider (or other invertebrate). They then develop to maturity within the spider’s body. At this point Gordius convinces the spider that it is in desperate need of a drink and sends it scuttling to the nearest puddle. Once there Gordius bursts forth from the spider’s body, in true Alien style, and re-enters the water to continue its life cycle. These large worms are frequently found by zoo keepers in animal water bowls. They do not affect the zoo’s regular inmates and are completely harmless, unless you happen to be a spider.

2)      Clistobothrium carcharodoni. This mouthful is a tapeworm that lives in the gut of great white sharks. Tapeworms produce eggs that develop into larvae which encyst in an intermediate host. This host is then consumed by the definitive host, thus completing the life cycle. In this instance the intermediate host is the dolphin. The larvae preferentially encyst in the muscles of the dolphin’s belly, as these are the particularly tasty ones targeted by sharks when they attack. In this way the shark not only gets a mouth full of Flipper but a mouth full of Clistobothrium as well.

3)      Euhaplorchis californiensis. This is a parasite of birds that uses killifish as its intermediate host. It gets into the fish’s brain and, in order to increase its chances of being eaten by the bird encourages the fish to swim conspicuously near the surface of the water, advertising its tastiness.

4)      Leucochloridium paradoxum. This flatworm employs a similar strategy when it gets into snails. The larvae enter the snail’s eye stalks and then wriggle about to look like little caterpillars that once again attract the bird definitive host.

5)      Toxoplasma gondii. This parasite has its home in the cat intestine but uses rats, among others, as an intermediate host. It gets into the rat’s brain, removing its innate fear of cat urine, replacing it with a deep desire to seek it out instead. You can guess the outcome.

6)      Guinea worm. In case you thought we were immune from this kind of manipulation, think again. The guinea worm begins life as a larva tiny enough to fit inside the common water flea. The flea is accidentally drunk by a thirsty human. Not being adequately equipped to survive the harsh environment of the human stomach, the water flea is dissolved away, leaving the guinea worm larva behind. It finds a soft, fleshy cavity to burrow into and starts growing. About a year after infection, the full sized guinea worm measures two to three feet long and decides it’s time to get out. It does this by burrowing to the surface of the skin and creating a blister. This causes a burning sensation, which makes the infected human want to dunk it in water. The rear end of the worm emerges from the blister and releases hundreds of thousands of larvae. They are eaten by water fleas and the whole thing starts all over again. Fortunately or unfortunately, depending on where you are currently living, the guinea worm is only endemic to Sudan, Ghana, Mali and Ethiopia.

You may have noticed the one thing all these characters have in common is that they are parasites. If you make your living by manipulation and stealing someone else’s resources and livelihood I guess you need to be cunning to survive. Perhaps humans are not so low on the cunning pyramid after all, as we’ve spent thousands of years doing just that to the Earth.

Dr. F. Bunny

For more fascinating information about the world of parasites see Ed Yong’s TED talk at http://www.ted.com/talks/ed_yong_suicidal_wasps_zombie_roaches_and_other_tales_of_parasites.

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