IT has been known since ancient times that nectar, usually secreted from specialized glands within flowers, is utilized by anthophilous (flower-visiting) animals for the energy-providing sugars that it contains. It is usually assumed that protein-making materials will be obtained elsewhere, from larval feeding (Lepidoptera), from pollen (Hymenoptera-Apioideae) or (by vertebrates) from insects. However, some butterflies are known to be attracted to decaying flesh, faeces, urine and stagnant water1 and well as sweat2, while many take phloem-sap from a wound or honey-dew excreted by aphids1. Moths are known to drink fruit juices, sweat, secretions from the eyes of animals, and even mammalian blood3. Unusual feeding-behaviour is shown by butterflies of the genus Heliconius which collect pollen, steep it in nectar, and subsequently ingest the amino-acids that diffuse from the grains4.