Some species of aphids have acquired the ability to synthesise red carotenoids by horizontal gene transfer from fungi. They are the only animals other than two-spotted spider mites and the oriental hornet with this capability. Using their carotenoids, aphids may well be able to absorb solar energy and convert it to a form that their cells can use, ATP. This is the only known example of photoheterotrophy in animals. The carotene pigments in aphids form a layer close to the surface of the cuticle, ideally placed to absorb sunlight. The excited carotenoids seem to reduce NAD to NADH which is oxidized in the mitochondria for energy.
