to blend in with their surroundings during vulnerable times like diapause (hibernation). When picked up, the butterflies become rigid and hide their legs from view in order to decrease their chances of being recognised. Genetics of colour patterns Pigmentation and structural coloration Variation in coloration of Lepidoptera wings is caused by different structural and pigment components. These differences cause light to scatter in different ways, leading to the different colours. In the common brimstone, wing scales scatter light incoherently due to ovoid-shaped structures called beads that contain pigments. Due to these pigments, the beads absorb short wavelength light and scatter longer wavelengths outside of the pigment absorption spectrum, such as light in the complementary wavelength range. Through chemical extraction and analysis, two possible pigments have been identified that may contribute to the common brimstone's wing coloration. Xanthopterin is responsible for the sulphur yellow colour of the male wings since it absorbs in the violet range. Leucopterin was extracted from the white wings of females. The difference in wing pigmentation contributes to the distinct iridescence patterns of males and females. Iridescence occurs due to visualised changes in coloration from the scattering of ultraviolet light. A male-only pattern of coloration due to this iridescence is seen exclusively under ultraviolet light, since females absorb light on the ultraviolet spectra. The presence of exclusively leucopterin in female wings explains the lack of iridescence in female common brimstones, since leucopterin absorbs only in the ultraviolet range. Therefore, the wings do not reflect and consequently do not scatter any ultraviolet light like male wings do. In males, iridescence is indicated in that the wing pattern appears to visually change depending on the position of the ultraviolet light shone onto the wing. At some angles, a male pattern is seen, while at other angles, a female lack of pattern is seen. This is referred to as the "gynandromorphic effect." This demonstrates that the pattern appears to be optical, rather than pigmental, as the effect is only seen at certain angles and distances of light and changes with positions. If it were pigmental, these changes would not cause differences in iridescence. The structural coloration of the male dorsal wings is affected by environmental factors. There is an increase in ultraviolet coloration coverage with increasing temperature, increasing precipitation, and decreasing latitude. This has been possibly attributed to several factors, such as the greater abundance and quality of resources in