The gustatory receptor (Gr) family of insect chemoreceptors includes receptors for sugars and bitter compounds, as well as cuticular hydrocarbons and odorants such as carbon dioxide. We have annotated a total of 65 Gr genes from the silkworm Bombyx mori genome. The Gr family in the silkworm moth includes putative carbon dioxide receptors and sugar receptors, as well as duplicated orthologues of the orphan DmGr43a receptor. Most prominent in this 65-gene family, however, is a single large expansion of 55 Grs that we propose are predominantly 'bitter' receptors involved in perception of the large variety of secondary plant chemicals that caterpillars and moths encounter. These Grs might therefore mediate food choice and avoidance as well as oviposition site preference.