Which Flies Appear Green?
While many insects display green hues, the flies most commonly observed with a striking green coloration belong to the blow fly family, Calliphoridae. Among these, the common green bottle fly, Lucilia sericata, is widely recognized for its brilliant, metallic blue-green or golden appearance. These flies measure 10 to 14 millimeters in length, slightly larger than a common house fly. Their bodies are characterized by black markings, clear wings with light brown veins, and black legs and antennae.
Green bottle flies are found globally in temperate and tropical regions, often inhabiting areas with warm and moist climates. They are frequently seen near carrion, feces, and garbage, as females lay their eggs in decaying organic matter. Another species, Calliphora vomitoria, sometimes exhibits green coloration. Like green bottle flies, they are scavengers, laying eggs on decaying matter.
How Flies Get Their Green Color
The vibrant green color observed in many flies, particularly the metallic sheen of bottle flies, does not come from green pigments within their bodies. Instead, this striking coloration is a result of a phenomenon known as structural coloration.
Structural coloration occurs when light interacts with microscopic physical structures on the surface of an organism. In flies, these structures are found on their outer covering, called the cuticle, which is made of chitin. The cuticle possesses intricate nanostructures, such as multiple layers or tiny gratings, that are precisely spaced. When light hits these structures, certain wavelengths are reflected, while others are canceled out or absorbed.
This selective reflection and interference of light creates the vivid, often iridescent colors. The specific hue, such as green, depends on the exact size, shape, and arrangement of these nanostructures. Because the color is produced by light interaction with these structures, the perceived color can shift depending on the viewing angle, creating a shimmering effect.
The Purpose of Green Coloration
The green coloration in flies serves several evolutionary and ecological functions. A primary advantage of this metallic green hue is camouflage. The iridescent green can help these flies blend into their natural environments, such as foliage, grass, or other vegetation. This blending makes them less conspicuous to predators, increasing their chances of survival.
The reflective quality of their cuticle, which produces the green color, might also play a role in thermoregulation by reflecting sunlight and helping to regulate body temperature. Beyond camouflage, the bright coloration could also serve as a form of signaling within the species. Vivid colors in insects can sometimes be involved in intraspecific communication, such as attracting mates. This visual cue might help individuals recognize and locate potential partners, contributing to reproductive success.