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Butterflies
A butterfly can be trained to land on a yellow portion of the colored grid. Moreover, butterflies have color constancy (like humans) and will still recognize yellow even if the illuminating light changes considerably (color constancy).
Plants have evolved their flowers to make it easy for butterflies, and other pollinators to feed on their nectar. Plants attract potential pollinators many ways, including color, scent, reflectance, size, outline, surface texture, temperature and motion. Plants which do not depend on insect or bird pollination are unlikely to have showy or scented flowers.
To attract the potential pollinator to that particular blossom, availability of nectar has to be advertised to the butterfly. This is displayed in the color of the petals. The color of the nectar guide of Aesculus hippocastanum changes from yellow to red when nectar is no longer in production. Further assistance is available in the form of nectar guides, also referred to as "pollen guides" or "honey guides.". These are usually a visual contrast, either in form or coloring. Sometimes we can see these patterns, and sometimes they are in the ultraviolet.
One of the best known flowers with the bulls-eye effect in ultraviolet is the black-eyed Susan, Rudbeckia hirta , which contains compounds absorbing strongly between 340 nm and 380 nm. The petals of the Black-eyed Susan, a large daisy-like flower, appear plain yellow to humans while appearing to have a very dark centter to insects. COMPARE VIS & UV.
The Japanese yellow swallowtail butterfly Papilio xuthus uses color vision when searching for food. It has a compound eye structure, and has at least five types of spectral receptors (UV, violet, blue, green, red)., suggesting that they have color constancy. In nature, these butterflies feed on nectar provided by flowers of various colors not only in direct sunlight but also in shaded places and on cloudy days. Butterflies vary widely in their sensitivity of light, and are considered to have the widest visual range of any animal. A pentachromatic visual system (i.e. the eyes contain 5 different types of cell which react to different bands of light), has been reported in Papilio xuthusAtrophaneura alcinous has a visual range from at least 400 nm to 700 nm, while Heliconis sara has a range from 310nm to 650nm.
Views:
Invisible patterns are revealed on this blackeyed susan and Cleopatra butterfly when the ultraviolet light is seen.
To the human eye many butterflies appear the same, but the butterflies themselves can often identify each other quite easily from ultraviolet markings. Shown above is the yellow Cleopatra butterfly Goneopteryx cleopatra. For example the males and females of Eurema lisa, the small sulphur butterfly, differ only in the ultraviolet region, the males being strongly ultraviolet reflective and the females unreflective in ultraviolet. The need for significant differences in appearance exists only in butterflies which are palatable to birds.
The ultraviolet patches on some butterflies are directionally iridescent, as a result they appear to flicker in flight. This flickering is thought to have an important role in butterfly behavior and communication.
Butterflies tend to avoid the color green in their feeding behavior, but are attracted to it during egg laying. The next generation need to be placed near a good source of food as caterpillars have a voracious appetite. The green photoreceptors are instead used for the detection of movement.
