The horse-chestnut leaf-mining mothThe moth whose caterpillars are causing the damage to horse-chestnut trees is the horse-chestnut leaf-mining moth, which has the scientific name Cameraria ohridella.
It is known as one of the 'micro moths', to distinguish it from the typical 'macro moths', which are the larger moths often attracted to light.
|A mating pair of horse-chestnut leaf-mining moths. © Dave Kilbey|
The adult mothThe adult moth is tiny - just a few millimetres long - and very attractive, with white stripes on glossy bronze wings. Many people we have spoken to are surprised that the moth is so small. When the adults emerge, there can be so many flying close to a horse-chestnut tree that the tree appears to shimmer.
Its leaf-mining larvaeIt is the larvae (or caterpillars) of the horse-chestnut leaf-miner that do the damage and feed on the leaves of the horse-chestnut. Many caterpillars are external feeders, but the horse-chestnut leaf-miner is different. Its larvae actually live inside the leaf and they 'mine' the leaf forming what are called, unsurprisingly, leaf mines. As they feed on the green tissue on the inside of the leaf, they leave the upper and lower layers of the leaf (the 'epidermis) intact, so the larvae remain protected.
The remaining epidermis of the leaf is translucent, which is why the leaf mines look whitish when they are fresh. After a few weeks the epidermis of the leaf mine dies and turns brown.
Each larvae produces a singe leaf mine, which eventually ends up about the size of half a person's finger. When infestations are large, the mines coallese and the larvae form groups searching for the remaining green tissue.
The larvae have incredible adaptations for living inside a leaf. They are have flattened so they can easily move about in the leaf mine and they have chisel-shaped heads with pointed moutparts so they can easily eat the fresh green tissue at the edge of the leaf mine.