Red-absorbing visual pigment of butterflies.

Noninvasive photochemical and physiological experiments with intact butterflies of 17 species showed that nine species have a rhodopsin absorbing maximally at 610 nanometers, contained in retinular cells that are maximally sensitive at 610 nanometers. This is the longest-wavelength visual pigment known for an invertebrate. Eight species of butterflies lack the 610-nanometers rhodopsin. All species possess a rhodopsin absorbing maximally in the green region of the spectrum.