The website Pest Management Handbooks (Pacific Northwest) says, “The serpentine madrone miner adult is a tiny moth. Larvae of this leaf- and twig-mining moth blaze sinuous, serpentine mines across the surface of leaves. Although damage might be unsightly on individual leaves, they do not affect the long-term health of the tree.”

As we know, I don’t think it’s unsightly. I love these patterns and the history they reveal. But I’m glad to know that the leafminer (whose scientific name, Marmara arbutiella, signals its special relationship with the Arbutus genus) gets what it needs without causing real harm to the tree. My daughter tells me this variety of symbiosis, in which the relationship is beneficial to one species, and neither helpful nor harmful to the other, is called commensalism.