When the leaves are just on the turn in the autumn, we think it’s the best time to be in the woods – not only to enjoy the beautiful colours, but also to be looking for some of our more under-recorded native fauna. Have you ever noticed leaves on trees, such as oaks and hazel, that have been carefully rolled over, or that have curious blotches or silver wiggly lines on them? These are signs of fascinating lives going on within these leaves – whether it is in a woodland or in your garden there are leafminers at work.
Leafminers represent a cross-section of specialists from several species groups such as moths, flies and wasps. We’re on the lookout for micro-moth leafminers so we will tell you a bit about these. Most species of leafminers have one or two species of plant or tree that they will feed on. The adult micro-moth will lay its tiny egg on the leaf of its food plant and when the larva hatches from its egg it burrows in to the leaf. It will then spend some or all of its larval phase between the epidermal or outer layers of the leaf, feeding in safety away from predators’ eyes.
The mines themselves vary in shape and size and this, along with knowing what the food plant is, enables us to identify a majority of the leaf mines made by micro-moths, although some need to have the adult reared to confirm which species has been growing inside when it finally hatches out. There are a few different types of mine including blotch, gallery and blister – some are lined with silk, some create folds in the leaves and some have small windows that have been created by feeding larvae – they all have their own distinguishing features which, with the aid of a key, can point towards which species it is.
If you hold the leaf up to the light you can often see the inhabitant busily eating away at the juicy green tissue within. As the larva feeds it usually leaves a trail behind it, which gets wider as they get fatter. When the larva has filled its boots, it will emerge through an exit hole and pupate, sometimes dropping to the ground and pupating in the soil. Some of the later stages of the larvae come out of the leaf and carry on feeding in the safety of a self-constructed funnel-like shelter that they roll in the leaf until they are ready to pupate.
Further reading: www.leafmines.co.uk – your guide to British and European leafmines