This autumn the upper surface of many of the leaves on young beech trees around here are carrying these cylinrical, hairy galls caused by a midge called Hartigiola annulipes that laid its egg in the leaf surface back in the spring. Opening them up reveals the hollow chamber inside with the larva developing down at its base. In a week or two, when it's mature, the gall will separate and fall from the yellowing leaf, shortly to be buried under a carpet of fallen leaves. The larva will pupate there, until the adult midge emerges in spring, at just the right time to lay its eggs in the soft tissue of a newly expanded leaf.
Gall sectioned vertically.....inside, there's a large, hollow chamber
The larva, tucked in here down at the bottom of the gall chamber, still has plenty of room to grow.
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