Meet the green hairstreak (Callophrys rubi), a small, widespread butterfly native to Europe and Asia. It holds a unique title in its region as the only butterfly boasting a vibrant green underside, providing flawless camouflage among sun-dappled leaves. Remarkably, this brilliant metallic hue is an optical illusion; rather than a green pigment, the color is created by structural coloration—the diffraction and interference of light passing through microscopic, lattice-like structures within the wing scales. When perched, it tightly folds its wings to hide its dull brown uppersides, revealing only its iridescent camouflage until it takes flight. While the adult is a gentle nectar-sipper, the life of a green hairstreak caterpillar has a darker side. These plump, slug-like larvae feed on a wide variety of plants like gorse, bramble, and bilberry—but newly molted individuals are opportunists, occasionally cannibalizing their slower, vulnerable peers. Because of their masterful camouflage, spotting these butterflies in the wild is incredibly difficult. I counted myself incredibly lucky to catch a flash of green in mid-air and trace it to a brief rest on a forest path, giving me just enough time to lock focus and secure some beautiful shots.