Two galls
| Beech gall midge , Mikiola fagi | Red nail gall mite , Eriophyes tiliae |
|---|---|
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in the past (half?) year, I've been gifted with the opportunity to see the beech gall midge Mikiola fagi and the red nail gall mite Eriophyes tiliae without having to spend time looking for them. Both galls appeared on trees I pass by on my everyday commute.
Galls (or, cecidia) are fascinating. For both these galls, tiny invertebrates induce the formation of galls by chewing the leaf & secreting compounds like hormones. This mix of stressors causes the plant to grow into a gall. The gall forms a perfect living-spot for the invertebrates, protecting them, the bugs effectively "growing" their own "house". so many critters induce galls, and the variety in gall appearance is incredible and colorful.
Both M. fagi and E. tiliae spend the warmer seasons in their galls and overwinter elsewhere (the soil, and in tree bark, respectively). They are associated with particular trees, enough that their names reference this relationship — M. fagi beech galls on Fagus beech & E. tiliae galls on Tilia lime/linden. Apart from how the galls look, the tree that they're on is an identifying feature. both these trees are deciduous, growing leaves in the spring & dropping them in autumn, which explains the overwintering phase of the gall-formers' life cycles.
I find the galls immensely beautiful, especially the bright red color of E. tiliae. However, it seems this opinion isn't widely shared. When first learning about these gall-formers (when doing my initial ID-ing), many many articles center the question of "How do I get rid of them?"
...though, refreshingly, that question was always answered with something along the lines of: The galls don't harm the plant, so we haven't figured out a "cure" & we're unlikely to ever spend the effort to do so. It's nice that for once, a purely-cosmetic "pest" is left to mind its own business, though as always the desire to "cure" the condition despite it being harmless is... ugh.
though there are certainly other gall-appreciators if we look towards the scientific community instead of the gardening community. There is a field of gall studies, Cecidology, with its own journal. As any cecidologist (professional and hobbyist alike) knows, galls are not only beautiful but very important. Looking at the above two acquaintances-of-mine, many beech gall midges are noted to predate on common crop pests according to the Agricultural and Horticultural Development Board (UK). At the moment, looking into managing hedgerows to provide a habitat for predators of crop pests is a topic of much interest (here's a paper if you're interested) so knowing that specific trees support pest-eating gall-formers can inform this research/practice.
Think galls are cool & want to look at more? The British Plant Gall Society (the Cecidology journal people) have a website which has photo galleries to look through.
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thanks for reading!🪱🦀
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