A leaf miner is any one of numerous species of insects in which the larval stage lives in, and eats, the leaf tissue of plants. The vast majority of leaf-mining insects are moths (Lepidoptera), sawflies, and flies (Diptera). Some beetles also exhibit this behavior.
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
Frass refers loosely to the more or less solid excreta of insects, and to certain other related matter.
Bedstraw hawk-moth caterpillar leaving the frass behind
Typical sculpting of a frass pellet of a large caterpillar
A thistle tortoise beetle larva carrying a mass of its own frass as a repugnatorial defence.
Galleries of various species of wood-boring beetles typically are stuffed with frass