Historical collections of butterflies (Lepidoptera: Hesperioidea and Papilionoidea) are an absolutely essential resource to investigate current and past biodiversity at any given place in space and time. This is particularly true for the Neotropics, where the richest butterfly fauna of the world is found. Collections accumulated in the major world museums since the late 16th century, allow partial reconstruction of the structure of butterfly communities in many natural habitats which have since been profoundly altered or even irretrievably lost through human intervention. This is best exemplified by the peerless collections held by The Natural History Museum, London.