Tales of the roaming dead – in your backyard.

Warning: Not safe for work – you wouldn’t want to feel nauseous in the office, do you?

Themes of zombies and the living dead have never failed to capture people’s imagination. Zombie-genre films such as Night of the Living Dead and 28 Days Later are continuously churned out by Hollywood producers to feed the insatiable appetites of consumers for thrill and excitement. One might think that zombies are restricted only to the big screens and science fictions; they are terribly wrong. In reality, zombies do roam the earth, and they might just be in your backyard.

The zombie and the parasites

The zombie and the parasites

Parasitic wasps have always been a fascinating research area for scientists. These wasp injects its eggs into the caterpillar host and the newborn larvae will feed on the caterpillar’s body fluids and grow inside the host. Think of it as a mobile food van with all-you-can-eat buffet for these hungry young maggots.  Wasp Glyptapanteles can inject up to eighty eggs into the caterpillar host. (Brahic, 2008) When the larvae are fully grown, they emerge out of the caterpillar’s skin to spin their cocoons and undergo pupae stage. It might be every caterpillar’s dream to become a beautiful butterfly, but alas, this unfortunate one will never be. In addition to inject her eggs, the parasitic wasp also injects a plethora of virus particles into the host, hay-wiring its immune system, causing it to fail to pupate and dies as a caterpillar. (Beckage, 1997)

What’s even more intriguing, however, is that the wasp larvae appears to have manipulative control over its host. Once the larvae emerged out of the caterpillar and become cocoons, the caterpillar stays stationary and does not move or feed, as if it is watching over these vulnerable cocoons.

Click the link to see zombie caterpillar in action : Zombie caterpillar controlled by voodoo wasps

As seen in the video, if the caterpillar is infected by parasitic wasp, its behavior drastically changes and will actually defend the wasp cocoons vigorously if a predator approaches. The caterpillar will stay alive until the adult wasp hatches.

This is no mere coincidence: in an experiment conducted by Ame Janssen of University of Amsterdam, it is discovered that the majority of the parasitic caterpillars will defend the cocoons by thrashing their head vigorously to knock the incoming predators off the branch while uninfected caterpillars are totally oblivious to the predators. Furthermore, the cocoons guarded by the parasitic caterpillars have double the survival rate of its unguarded counterparts. (Brahic, 2009) This further proves that the wasps have a profound manipulative influence on its caterpillar host.

If you think such atrocious acts of parasitism does not occur in our area, think again. A species of parasitic moth of family Ichneumonidae has been spotted in Bukit Timah Nature Reserve, parasiting its host Pergesa Acteus (Leong, 2009)

So next time when you walk through the forested areas in Singapore, be extra cautious. Who knows, you might be stepping into a zone of zombie caterpillars and their parasitic hosts.

References:

  1. “Zombie caterpillars controlled by voodoo wasps”, Catherine Brahic, NewScientist, 04 June 2008. URL: http://www.newscientist.com/article/dn14053 (accessed on 14 April 2010)
  2. “Zombie caterpillar controlled by voodoo wasps”, NewScientistVideo, Youtube, 03 June 2008. URL: http://www.youtube.com/watch?v=7UkDMrG6tog&feature=player_embedded (accessed on 14 April 2010)
  3. Beckage, N.E, The Parasitic Wasp’s Secret Weapon, Scientific American, Nov 1997, 277(5):  82-87.
  4. Caterpillars Beware: Parasitic Wasps Come in a Wide Variety”, Andrew Moseman, Discover Magazine, 02 Sep 2008. URL: http://blogs.discovermagazine.com/discoblog/2008/09/02/caterpillars-beware-parasitic-wasps-come-in-a-wide-variety/ (accessed on 14 April 2010)
  5. “Parasitized and Expired Hornworm”, Wormwould. Flickr. URL: http://www.flickr.com/photos/onthespiral/1245492578/ (accessed on 14 April 2010)
  6. Leong, T.M, Rozario, V.D, Larval development and metamorphosis of the hawkmoth, Pergesa Acteus in Singapore, Nature in Singapore, 2009 (2): 329-338

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