Most adults feed on nectar, although a few tropical species feed on eye secretions, and the death's-head hawkmoths steal honey from bees. Night-flying sphingids tend to prefer pale flowers with long corolla tubes and a sweet odor, a pollination syndrome known as "sphingophily". Some species are quite general in visitations, while others are very specific, with the plant only being successfully pollinated by a particular species of moth. Orchids frequently have such specific relations with hawk moths, and very long corolla tubes. The comet orchid ("Angraecum sesquipedale"), a rare Malagasy flower with its nectar stored at the bottom of a tube, was described in 1822 by Louis-Marie Aubert du Petit-Thouars, and later, Charles Darwin famously predicted there must be some specialized moth to feed from it: