Know thy host

Picking the right spot to lay eggs is a challenge shared by many insects.  While most adult insects can fly, immature insects tend to be more limited in their movement.  Therefore, in addition to the safety of her offspring, the mother must ensure the availability of the right food -- and in adequate amounts.

A common aspen leaf miner (Phyllocnistis populiella) about to run out of leaf to eat.

Perhaps the mother of the leaf miner larva above should have chosen a bigger leaf.  Yet, young (and thus small) leaves may confer their own advantages, including being more tender and consequently easier to eat.  Indeed, young leaves are often preferred by a variety of herbivores.

On a side note, how does one identify an insect that is still inside a leaf?  The trick is to know the leaf.  Since leaf miners tend to be specialized on one or a small number of plant species, identifying the plant can lead to the identity of the leaf miner.  For example, identifying the leaf above as belonging to a quaking aspen (Populus tremuloides) quickly led to the identification of the larva inside.  Even when more than one leaf miner species uses a plant, the leaf miners will usually differ in the type of mine they create (see some other examples here and here).