Leaf mines

All the leaves on the local Horse chestnut trees are looking like this at the mo, it is the result of the larvae of the Horse Chestnut Leaf-miner moth (Cameraria ohridella).
These moths were first found in the UK in south-west London in 2002 and since then have been spreading rapidly. The larvae mine between the upper and lower surfaces of the horse chestnut leaves, causing these characteristic brown blotches, often many to one leaf. It does make the trees look interesting, if not somewhat unsightly, but it doesn't seem to affect their survival.