During my last visit to Nantucket for my survey of gall-making and leaf-mining insects on the island, I found a patch of buttonbush (Cephalanthus occidentalis) with an abundance of leaf mines that I didn’t recognize. Some leaves had linear mines, some had blotch mines, and some, like the leaf below, had both. I suspected (correctly, as it turns out) that the larvae of a single species of moth first make linear mines, then often pop out of the leaf and enter somewhere else before forming a blotch mine.
I stuffed a number of mined leaves into a bag with the hope of raising the adult insect. Ten days later, I checked the bag, and to my dismay it was full of droppings from caterpillars that were much too large to have been leafminers. One of them had a fancy pink dorsal stripe…
…and one of them did not.
As you can see in the above photo, they were rapidly devouring the leaves. I picked through what was left of the leaves and isolated the ones that still contained leaf-mining larvae in a vial. A week later, both of the big caterpillars had pupated.
Meanwhile, the leafminers were abandoning the leaves and getting ready to pupate.
Their pupae were enclosed in white cocoons, hidden between the leaves.
Two weeks after I collected the leaves, the first adult leafminer emerged.
Terry Harrison confirmed my impression based on the information on his website that this little moth is Mompha solomoni (Momphidae or Coleophoridae: Momphinae, depending who you ask), only recently (2004) recognized as distinct from its close relative, Mompha cephalonthiella. One ecological difference between the two species is that early spring generations of M. solomoni bore in the shoots of their host plant whereas M. cephalonthiella larvae are leafminers throughout the year.
Another two weeks passed, and one of the leaf-munching caterpillars emerged as an adult.
This moth turns out to be Ledaea perditalis (Erebidae), the “lost owlet.”
It’s not uncommon for tiny insects to emerge from unseen galls or leaf mines in plant material I collect when trying to raise something else, but accidentally raising a macro-moth from (apparently) an egg doesn’t happen to me too often.