Monarch Manoeuvre

Hanging in a 'J'

Imagine you are hanging upside down, zipped firmly into a sleeping bag which is attached to a strong clothes line. You are also blindfolded and your arms are tied firmly behind your back.

Somehow you manage to free your legs and get them out from inside the bag and fasten them onto the same clothes line. You then make the sleeping bag drop away, still with your arms disabled.

Sounds far fetched, doesn’t it. Every Monarch butterfly pupa does this manoeuvre as part of changing from a caterpillar.

Starting off as an egg about half a mm in diameter, the hatched caterpillar grows steadily until about 40mm long. It then attaches its rear feet to a twig or leaf by a silk pad spun from its mouth and hangs in a J shape for about 24 hours.

The caterpillar straightens and its skin splits along the back and starts to shed. The chrysalis wriggles, forcing the skin up towards the rearmost legs.

While hanging by just part of the skin its cremaster, a ‘black stalk’ with minute hooks on the end, is pulled down from within the skin and around the outside onto the silk pad.

Violent writhing then entangles the hooks into the silk and also causes the skin to fall away. With time, the chrysalis settles into its distinctive shape awaiting transformation into a beautiful butterfly.

The survival and continuation of this species depends upon the success of this hazardous manoeuvre, yet it is performed millions of times a year across many countries of the world.

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