Many a slip

twixt bug and blip....

I've been watching Large Cabbage White butterfly caterpillars travelling up the sides of the greenhouse. Having reached maturity they  leave off munching my Brassicas  and seek a dry spot to pupate - under an overhang such as the greenhouse roof is ideal. Once there they attach themselves and let nature take its course as their soft skins harden and their shape changes  - they pupate (pupa mean doll in Latin). Sealed inside the pupa case some sort of magic turns the caterpillar into a butterfly - which will emerge to fly straight back to my cabbage plants, mate and if female,  lay eggs: so the process begins all over again.

Except for some caterpillars it doesn't.  For some, their journey to pupation is arrested. These unfortunates are hijacked by  ichneumon wasps  that sting and paralyze the caterpillar then lay their eggs in or on  it. The larvae emerge and eat the (still living) ready-meal...

Unpleasant though this sounds, without parasitism there would be a lot more caterpillars and other insect pests attacking our food crops. Parasitic insects are reared and sold to growers with the purpose of reducing the numbers of pests and the damage they do.

More about parasitic wasps here.