Wild type fruit flies are yellow-brown, with brick-red eyes and transverse black rings across the abdomen. The brick-red color of the eyes of the wild type fly are due to two pigments xanthommatin, which is brown and is derived from tryptophan, and drosopterins, which are red and are derived from guanosine triphosphate. They exhibit sexual dimorphism; females are about 2.5 mm (0.10 in) long; males are slightly smaller with darker backs. Males are easily distinguished from females based on colour differences, with a distinct black patch at the abdomen, less noticeable in recently emerged flies, and the sexcombs (a row of dark bristles on the tarsus of the first leg). Furthermore, males have a cluster of spiky hairs (claspers) surrounding the reproducing parts used to attach to the female during mating. Extensive images are found at FlyBase. Drosophila melanogaster flies can sense air currents with the hairs on their backs. Their eyes are sensitive to slight differences in light intensity and will instinctively fly away when a shadow or other movement is detected.