The horror, the horror
Okay, once again I’m late with this week’s blog. But on the plus side, I actually have a proper subject this week, and that’s how nature just keeps on coming up with the best and most bizarre types of parasitism, trumping anything that human writers can think up.
Now parasites are all over nature, everything that walks, crawls or flies has some form of parasite living on or in them. Often, these parasites are fairly benign, causing little or no problems for the host organism. Indeed, the term parasite actually refers to organisms that live within a host for an extended period of time, usually without causing much damage. The term parasitoid, on the other hand, refers to organisms that usually end up killing their host, because they only act as a parasite when young.
One example is parasitoid wasps, which lay their eggs inside living caterpillars. After hatching, the resultant wasp larvae feed on the caterpillar from the inside, before bursting out when grown to sufficient size. A fictional version of this process appears in the film Alien, where an alien larva grows inside John Hurt before bursting out of his stomach during lunch. If you’re a caterpillar, though, Alien is more of a shocking documentary than a horrific science-fiction movie.
Despite their unsavoury behaviour, parasitoid wasps are actually very useful creatures, often used as environmentally-friendly pesticides for controlling caterpillars that feed on agricultural crops. But Brazilian researchers recently discovered a species of parasitoid wasp that demands a whole lot more from its caterpillar host.
Usually, the caterpillar dies once the wasp larvae burst out of it, but in this case the researchers discovered that the caterpillar stays alive to defend the larvae from attack by predators. So not only is the caterpillar devoured from the inside, but it then has to protect its devourers after they’ve burst out.
This would be like John Hurt physically attacking his ship-mates as they try to hunt down the alien, all the time with half his insides hanging out. Alien may be a classic film, but I think that the director Ridley Scott missed a trick by not including such a scene.
The researchers, who reported their findings in a recent issue of the journal PLoS One, think that caterpillar acts in this way because a couple of larvae remain inside it and seemingly dictate its actions. Almost like they’re controlling a puppet.
There are numerous other examples of parasites controlling the behaviour of their hosts in this way. For instance, the parasitic worms known as flukes initially infect ants. During the night, ants usually return to their nests, but those infected with flukes instead climb to the tops of blades of grass. Here they are eaten by grazing sheep, which are the flukes’ main host. Other parasitic worms make their insect hosts commit suicide by jumping into water, allowing the adult parasites to reproduce.
Translate this type of parasitic behaviour to humans and you’ve got some great films. All of which shows that when it comes to horror, nature really does come up trumps.
