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.
Sermons in Stones 
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May 30, 2022 at 7:35 am
Erp
I note the specific name, menziesii of Arbutus menziesi, is shared with an earlier tree you did, Pseudotsuga menziesii aka Douglas-fir. The name is in honor of Archibald Menzies (1754-1842) who was a naval surgeon and/or naturalist and served with Vancouver. Among other places he visited was the San Francisco area in 1792, and though he did not visit Mission Santa Clara with Vancouver and thereby cross Palo Alto, he did write up what others saw (including trees).
Menzie, Archibald, and Alice Eastwood. 1924. “Archibald Menzies’ Journal of the Vancouver Expedition.” California Historical Society Quarterly 2 (4): 265–340. https://doi.org/10.2307/25177726.
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May 30, 2022 at 12:22 pm
Karen Skold
leaf miners are not so innocent when they get into leafy greens like spinach. They do kill the leaves if they eat enough, and a baby spinach plant is a lot less resilient than a madrone tree! I don’t try to grow spinach any more in my garden for that reason.
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May 30, 2022 at 1:05 pm
Amy Zucker Morgenstern
Sorry about your spinach!
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