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Published online by Cambridge University Press: 31 May 2012
I send you a few specimens of an insect which I have found parasitic on the larvæ of P. cardui. For several successive summers I have reared a number of these caterpillars, with which our thistles in most seasons abound. I observed variations in size and color of the larvæ found feeding on the same plant, which led me to suppose that they might not belong to the same species.
* This insect has been kindly determined by E. T. Cresson, of philadelphia, as Ichneumon rufiventris.—Ed. C. E.