Given a choice, a fruit fly will seek a temperature optimum of 18°C. This behavior requires a biochemical signaling pathway apparently initiated by a heterotrimeric guanine nucleotide–binding protein (G protein)–coupled receptor. Given the similarity of these signaling events to those initiated by rhodopsin, the G protein–coupled receptor that senses light, Shen et al. (see the Perspective by Minke and Peters) tested the effects of rhodopsin mutations on temperature selection in flies and, surprisingly, found that it resulted in discrimination between temperatures within a few degrees of the optimal 18°C, independent of light sensation. One or more accessory molecules may also be required, as the rhodopsin molecule itself does not seem to be the temperature sensor.