My Field Studies Council Guide to plant galls in Britain explains that the gall midge Taxomyia taxi actually causes two types of gall on Yew trees. The least common, which looks just like a swollen bud, completes its life cycle in one year – I’ve yet to find any of these. But I was very pleased earlier this week to locate several examples of the artichoke gall, in which the same midge completes a two-year life cycle. Eggs are laid in May/June, the larvae crawl in to a leaf bud and stay there, barely growing, until the following summer. At that point, they grow rapidly, over-winter again as larvae, before pupating and hatching the following May. I couldn’t find any explanation for the different life cycles.
Not wanting to kill the creatures inside, I haven’t opened up any of the galls I’ve found but, if you’re curious, as I was, about what’s inside the artichoke, the Plant Parasites of Europe website has some excellent images of the larva, the pupa and the adult fly.
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