LEAF MINERS

The artistic hand of nature paints these pale lines on leaves of various plants.

Above on red valerian and below on hogweed.  These are the trails of leaf mining caterpillars, the larvae of small micro-moths that specialise in a particular plant.  The egg is laid between the upper and lower membranes of the leaf.  When it hatches, the larva eats its way through the juicy layer in between, like eating the cucumber out of a cucumber sandwich but leaving the bread untouched.

My favourite is the bramble leaf miner.  You can see three trails inside the leaf below, each tunnel getting wider as the larva gets fatter. 

It pupates inside the leaf and then emerges as a moth to start the process all over again.