Leaf miner

The vast majority of leaf-mining insects are moths (Lepidoptera), sawflies (Symphyta, a paraphyletic group which Apocrita (wasps, bees and ants) evolved from), and flies (Diptera).

Like woodboring beetles, leaf miners are protected from many predators and plant defenses by feeding within the tissues of the leaves, selectively eating only the layers that have the least amount of cellulose.

When consuming Quercus robur (English oak), they also selectively feed on tissues containing lower levels of tannin, a deterrent chemical produced in great abundance by the tree.

[1] The pattern of the feeding tunnel and the layer of the leaf being mined is often diagnostic of the insect responsible, sometimes even to species level.

For example, lambsquarter and columbine will distract leaf miners, drawing them to those plants and therefore reducing the incidence of attack on nearby crops.

Leaf miner damage to a horse chestnut tree
Leaf with minor miner damage
Tomato with leaf miner damage
Leaf mines by the moth Phyllocnistis hyperpersea on a Persea borbonia leaf
Leaf miner trail on a fallen leaf in a Gondwana cool temperate rainforest. Note the initial thin width of the insect trail, becoming wider as the insect grows while it navigates around the leaf. Cryptocarya foveolata from Cobark Park, Barrington Tops , Australia
Horse-chestnut leaf miner (adult)
Phyllocnistis magnoliella in magnolia leaf.