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I was reading a book review yesterday. The book is called Wild Hares and Hummingbirds, and the reviewer said one thing he'd learned from it is that "our small tortoiseshell butterfly population is being significantly reduced by a parasitic fly which has recently appeared in Britain". Does anyone know the full story, please? I'm guessing it is a tachinid.

It wasn't a very glowing review of the book overall.

John Bratton