Insects are amazing in their diversity and range, there are insects found in almost every habitat that supports life: they live in the soil, in streams and ponds, on plants, high in the mountains, there are even insects that live in the Antarctic. The deep ocean is probably the only place where you will not find insects.
One group of insects specialises in living part of its life inside leaves in the tiny space between the upper and lower surface, they are known as leaf miners. They are the larvae of beetles, moths, flies and sawflies that lay their eggs on a leaf and the emerging larva or caterpillar tunnels inside where it feeds on the leaf tissue.
The outer epidermis of most leaves is see through to allow light in to the food producing green chloroplasts. As the insects eat the inner tissue their tunnels show through the surface. Different species feed on different leaves and their tunnels are often formed in distinctive patterns. Some just appear to wander about aimlessly while others work backwards and forwards methodically.
One of the most obvious leaf miners is the one that feeds inside the leaves of conker trees, the Horse Chestnut Leaf Miner. The adult is a tiny orange and white striped moth just 5mm long.
They over-winter as pupae in the leaf litter and adults emerge in April just as the trees are opening their new leaves. A female will lay 20-40 eggs along the lateral veins of the leaves. The eggs hatch after two to three weeks and the larvae will tunnel into the leaf causing brown scars.
After feeding and growing for four weeks, the larvae spin a silken cocoon inside which they will pupate. In summer, the new adults will develop and emerge after two weeks. There will be two or three generations across the season. The autumn generation go into a hibernation inside the fallen leaves to emerge the following spring.
Infestations can be very unsightly with leaves carrying many brown tunnel scars, but the tree copes with this. If you have conker trees and want to keep the moths down to a minimum then gather up and remove the fallen leaves so there are fewer new adults each spring.
Holly trees and hedges around the town frequently have Holly Leaf Miners, the maggots of a small fly. There are several different leaf miners of brambles, and scientists can tell them apart from the pattern of the tunnels but also how the larvae deposit their frass or poo in the tunnel.
Stigmella aurella, the Golden Pygmy Moth, creates a long winding tunnel that turns white with a central line of scattered frass dots. The Gold-edged Dot Moth eats out a short tunnel which has a purple margin and becomes packed with frass. The Raspberry Cane Maggot is a fly that uses various Rubus species to feed its young. The larvae start with a linear tunnel with neat parallel rows of frass but the tunnel opens out into a larger blotch with frass scattered irregularly.
There is a national leaf miner recording scheme at * https:www.leafmines.co.uk* and they welcome citizen scientists spotting leaf mines and sending them records. The website has plenty of information to help you tell which miner you have seen.
* The lifemines website has not been secured by its webmaster. You will receive a security warning if you try to connect to it and must make your own decision about doing so.
Ed Dolphin
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