Tunnels

I'm always curious about the tiny grubs that eat their way through the interior of plant leaves, leaving behind these squiggly patterns before exiting as tiny flies, so I joined a Facebook group called British leafminers.

I noticed these tunnels on primrose leaves  and now I'm informed  that they were created by the  larvae of Chromatomia primulae. 
Apparently you can distinguish the species of the larvae from the food plant, the pattern created and the location of the poo (a scattering little black dots in this case - not the big spots which are holes in the leaves.)

All this is good to know and, makes a welcome alternative to the 99% of the information that comes our way from other sources, social media or not. It's nice to connect with other people, however briefly, who find leaf miners interesting and want to pass on their knowledge.