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The Enemy Within

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Did you ever see the science fiction film "Alien"?  You know the famous bit where the monster bursts out of actor John Hurt's chest at the dinner table?  Gross.  Ever wonder if that could really happen?  In the world of the Braconids it's a regular way of life.

Braconids are a type of parasitoid wasp.  They come in many different shapes, sizes and colours, but the thing they all have in common is that they spend their childhood inside another species!

Female Braconids inject their own eggs into the bodies of other insects.  In the clip above you can see that a braconid, which goes by the scientific name of Apanteles glomeratus, has laid its eggs inside the caterpillar of a large white butterfly.

It's believed that the eggs are coated in a virus which disables the host's immune system, allowing them to hatch, and the larvae to grow, without the host knowing.  The larvae feed on the insides of the living creature, cleverly avoiding the vital organs, thereby keeping their host alive.

When the Braconid larvae are fully grown they eat their way out of their host by chewing a small hole in the skin.  The wasp larvae wriggle out and pupate beside their host.

You might think that after all this the unlucky host would just collapse and die.  Incredibly, the nightmare for the caterpillar is still not over.  As if in some zombie-like state, it spins a web of silk over the Braconid cocoons to protect them!

The developing cocoons are prone to attack by an even smaller species of parasitic wasp (hyperparasitoids) called Lysibia nanus.  To prevent this happening, the barely alive host caterpillar keeps watch over the developing parasitoids, flicking away intruders until the adult Braconid wasps emerge.

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