Have you ever noticed hairlike structures on leaves? Have you ever looked closer at the intersections of veins on the underside of a leaf and seen an extra tuft of hair density there? Although the group I volunteered with in high school liked to nickname these “hairy armpits” whenever we used them to differentiate between oak species, scientists call these high-density tufts of hair mite domatia.
These domatia (singular: domatium), essentially meaning home, encourage beneficial mites to take refuge in the especially protected corners. Although tufts are common, domatia can also come in the form of pockets with protective membranes, or tuft-pocket combination. In exchange for these homes, the mites forage on the surface of the leaves they live on, eating fungal spores and tiny herbivores that would otherwise damage the leaf.
A minute war is being waged on the underside of many a leaf, with wee mites and great trees working as allies. As the new leaves unfurl this spring, maybe take a moment to check if they have “hairy armpits” protecting them from the microscopic war being waged against them.
These microscopic threats may have a macro-scale impact, considering how many species deploy this “technique” of sorts to protect their leaves from harm. Mite domatia on the underside of leaves are nearly ubiquitous in deciduous forests, with 80% of common woody species in North America displaying this form of mutualism (see Ecology and Evolution Vol 15 Iss 4). Beyond such initial surveys of domatia and mite prevalence, research on mite domatia is limited.
Biology professor Mark McKone is investigating mite domatia on Boxelder (Acer negundo) trees in the Arboretum among other sex-based boxelder inquiries including flowering timelines.
- Cameron O’Connor ‘27, for Cole Student Naturalists
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