Growing Pains

You glide across your silky precipice,

Enticed by spasms at the edges of your kingdom;

You see nothing,

Just a loose thread caught in the wind.

Suddenly, movement –

You do not sense the vibrations

Beneath your feet,

But from the air above.

A shadow falls across your web as you

Dart across hidden ley lines and filaments.

A lucky escape.

Nothing more than a scratch.

A simple itch.

 

The itch begins to grow,

Your belly feels swollen,

Your legs lethargic.

You wake in the night with a cold sweat;

Unsure of what tomorrow might bring.

Recently you have begun to feel that

Your body is no longer whole;

That something is missing.

It will pass.

A simple itch.

 

You wonder if you have

Started to outgrow your skin;

Perhaps it’s time to cast off what you know.

Rebuild.

Start again.

First step – shelter,

A cocoon to hide you from the

World outside.

You spin a shiny dome of steel,

A sarcophagus in which to lie.

Your work is done.

Now time to sleep.

A simple itch.

The wasp larva proceeds to eat its host spider (Photo Credit: Marcelo O. Gonzaga).

This science poem is inspired by recent research, which has proposed the mechanism by which some wasps turn spiders into ‘zombies’ by injecting them with psychotropic substances.

Certain species of parasitoid wasps lay their eggs on spiders’ abdomens, with their larvae taking control of the spiders’ brains after hatching, forcing them to build an unusual web which acts as a cocoon for the wasp larva to take shelter in. The young wasp eats the spider when the web is done and then hides in this newly spun cocoon before emerging as an adult wasp. As these wasps are external parasites, their only access to the spider’s brain is via injections of psychotropic substances into the spider’s abdomen, which is then carried by the spider’s circulatory system to its central nervous system. Researchers have previously been unsure how this mechanism allows a single wasp species to induce such behaviour across many different spider host species.

This new research suggests that this mechanism likely involves the wasp hijacking the spiders’ molting behaviour. When spiders molt they shed their exoskeletons to allow them to grow a larger one. It takes a while for this new exoskeleton to harden, making them vulnerable to an attack by a predator, and therefore this process usually takes place in a special protective cocoon web. Spiders that have just built these cocoon webs tend to have high levels of a hormone called ecdysone in their bodies. This new research suggests the wasp larvae inject extra ecdysone into their host, essentially tricking it into thinking it’s time to molt, so that they create a cocoon web for the wasp larvae to take shelter in.

An audio version of this poem can be heard here:

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