Answer: A blowfly wing
The blowfly looks and behaves a lot like its housefly cousin but has a distinctive blue, green, or black metallic sheen. While they are best known as noisy pests, blowflies can actually help solve murder cases and repair nasty injuries. Because female blowflies lay eggs on fresh cadavers almost immediately, forensic scientists can look for deposited eggs and newborn larvae to determine when a person died. In medicine, the fly's young offspring are sometimes used in "maggot therapy" to prevent infection of open wounds by selectively consuming dead tissue and secreting enzymes that kill bacteria.