Weevil engineering

Taf Fechan Nature Reserve

Taf Fechan Nature Reserve

The Birch Leaf roller (Deporaus betulae)

The Birch Leaf roller (Deporaus betulae)

Imagine you’re a small black Weevil in a big world.  How do you protect your precious eggs and larvae from all the things that would want to eat them?

Some insects solve this problem by laying hundreds of eggs in the hope that some will survive by sheer chance and some have gone into heavy engineering.  Deporaus betulae is perhaps one of the most impressive insect engineers that I have come across at Taf Fechan, its larvae feed on Birch leaves and the female has evolved a brilliant way of protecting her young.   When she finds a nice juicy Birch leaf she starts cutting it into an exact curve and starts to roll the leaf up into a tube inside which she lays an egg.   This is entirely done by instinct, a genetically programmed perfect blueprint for this grand design has evolved (evaluate the size and shape of the leaf, start cut here, the curve sweeps at this angle, change of angle here, another change here, stop at the central leaf vein...) to turn a flat leaf into a tight roll, and it isn’t a simple task, a straight cut just won’t do, a curved cut is much easier to roll.   The Weevil itself is quite distinctive but difficult to find and when you do spot it it has the habit of dropping off the leaf to the ground at the slightest sign of danger (the two in the photo were “otherwise engaged” and didn’t notice me).   The rolled leaves are much easier to spot especially when they are older and have turned brown.