In animals such as the fruitfly, even minor deviations in environmental temperature can have major impacts on development and lifespan. Here we demonstrated that the ability of Drosophila melanogaster larvae to discriminate between the optimal temperature of 18 degrees C and slightly higher temperatures (19-24 degrees C) depended on the TRPA1 channel, which functioned downstream of a phospholipase C-dependent signaling cascade similar to that used in fly phototransduction. We propose that activation of TRPA1 through a signaling cascade promotes amplification of small differences in temperature and facilitates adaptation to temperatures within the comfortable range.