These stopped me in my tracks!
I’d enjoyed a nice amble around a local park and was on my way home when I spotted these incredible galls and just had to stop for some photos. The galls are caused by tiny mites that spend the cool winter months huddling in cracks on the tree’s bark, then head out on to the leaves when they sprout in the springtime.
The mites are leaf-sap suckers, and their sap sucking causes a chemical reaction in the leaf, which in turn prompts the leaf to produce these small, conical, hollow growths. The mites are incredibly tiny – less than 0.2mm long apparently – so they’re almost never seen, whereas their cosy gall homes can grow to 8mm long and, when they’re as bright as these ones were, are very obvious on the leaves.
I’m not sure which mites these are as I’m not sure which tree species this is. One mite species, Eriophyes tiliae, is the gall causer on Large-leaved lime trees (Tilia platyphyllos), Common limes (Tilia x europaea) and some hybrid Lime species, and another mite, Eriophyes lateannulatus, causes very similar galls on Small-leaved Limes (Tilia cordata) and hybrid Limes.