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5 Ways Parasites Hijack Their Hosts

By Robert Lamb, HowStuffWorks.com

HowStuffWorks

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5. THE HITCHHIKING PARASITE

Parasites have to spread their brood to other hosts, which generally means navigating one of two paths: sex or dinner. After all, animals are always eating one other, providing the savvy stowaway with a one-way trip to another organism's guts.

Yet many parasites eventually have to find their way back to their primary host. For instance, Toxoplasma gondii can only reproduce inside a cat, but must travel through feline fecal matter, then to mice and birds before making their way back to their breeding grounds.

To help matters out, a number of parasites reprogram their host to draw the attention of their primary host. Toxoplasma, for instance, makes rats crave cat urine, forcing them to seek rather than avoid the cats that would eat them. The lancet fluke Dicrocoelium dendriticum, makes its ant host ascend the tops of grass blades to attract birds.

Other hitchhikers take things to grotesque extremes. The tiny Myrmeconema neotropicum nematode worm causes its ant host's otherwise black abdomen to swell bright red. This attracts berry-seeking birds, which dive down to gobble up the hijacked ants. The parasitic flatworm Leucochloridium paradoxum inflicts a similar fate on snails, causing one eyestalk to swell up and turn bright green like a caterpillar. When a bird swoops down on the tantalizing morsel, the flatworm returns home to raise a family.

Count down 5 ways parasites hijack their hosts:

5. The Hitchhiking Parasite If a parasite is just along for the ride, it will devise devious ways to make its way back home.		4. I Wanna Be Your Tongue If food is a primary goal, why not just take out your host's tongue and plant yourself in its place?
3. Crab Hacking Sailors don't have to worry about barnacles breaching the hull, crawling inside and taking control. Crabs unfortunately do.		2. Suicide Worms Those "voices" in your head compelling you to drown yourself? Could be molecules planted by Nematomorph hairworms.
1. Parasite Protectors What could be more devious than being used as a food source for a parasite's larvae? How about being programmed to protect the little ones after they hatch.

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