Blow flies (family Calliphoridae) are recognized by their characteristic metallic sheen, often appearing in shades of blue, green, or bronze. These insects are classified as necrophagous, meaning they feed on and lay eggs in decaying organic matter. Their life cycle is closely linked to decomposition, giving them a significant ecological role as primary decomposers. The adult blow fly’s primary purpose is to locate suitable sites for their larvae (maggots) to feed and develop, a quest that drives their powerful sensory abilities.
What Attracts Blow Flies
The primary attractant for blow flies is decaying organic material, which provides the necessary protein and moisture for their offspring to complete development. The most significant and well-known attractant is carrion, or decomposing flesh, which includes dead animals and discarded meat scraps. In human environments, this attraction extends to other forms of biological waste. Garbage, particularly kitchen waste containing meat, spoiled food, and rotting vegetation, serves as a highly attractive breeding ground. Poorly managed waste containers, dumpsters, and recycling centers become prime targets for egg deposition.
Animal excrement, such as pet waste and manure, also draws adult blow flies seeking a protein-rich substrate. These unsanitary sources are often warm and moist, creating ideal conditions for rapid larval growth. In some species, like the black blow fly (Phormia regina), the attraction may even extend to fresh wounds on living animals, a behavior that can lead to a condition known as myiasis.
The attraction is not to the bulk material itself, but to the chemical byproducts of microbial breakdown occurring within the material. The decomposition process releases a complex blend of compounds that signal the presence of a viable larval food source. This chemical signature is what guides the female blow fly to the exact location where she will deposit her eggs.
Navigating to the Source
The incredible efficiency with which blow flies locate a food source, sometimes from distances up to 12 miles away, is due to their highly specialized olfactory system. Their navigation is almost entirely dependent on detecting volatile organic compounds (VOCs) emitted by decomposing matter. These VOCs are airborne chemical signals that function as an odor plume leading the fly to its destination.
The key odorants that signal decomposition are biogenic amines, particularly putrescine and cadaverine. These foul-smelling compounds are produced when microorganisms break down the amino acids lysine and ornithine within necrotic tissue. Specific olfactory receptor neurons located on the fly’s antennae are tuned to detect these molecules, allowing the insect to perceive the chemical signature of decay.
Beyond the initial attractants, the chemical profile of the source changes as decomposition progresses, and different VOCs become more dominant. For example, sulfur-containing compounds such as dimethyl disulfide and dimethyl trisulfide are powerful attractants, especially during the later stages of decay. These chemical shifts in the odor bouquet influence which species of blow fly will arrive and colonize the material at different points in time.
Once a fly has located the general area using its sense of smell, visual cues assist in the final approach and landing. Blow flies may use sight to detect color contrast, movement, or the physical presence of a potential host material against the background environment.
Reducing Blow Fly Presence
Managing blow fly populations effectively requires eliminating the sources that attract them in the first place. The most effective strategy is meticulous sanitation, which removes the necessary breeding substrate for the larvae.
Sanitation Practices
To interrupt the reproductive cycle and reduce the overall presence of flies, focus on these sanitation practices:
- Promptly and thoroughly clean up any animal waste from yards or outdoor areas, as feces is a significant attractant.
- Secure all outdoor garbage containers with tight-fitting lids that prevent flies from accessing the contents.
- Remove refuse frequently and use sealed bags for kitchen scraps, especially those containing meat.
- Clean the garbage cans themselves regularly to eliminate any residual organic material or liquid that may cling to the sides.
- Locate and remove any potential sources of carrion, such as dead rodents or birds, immediately.
- Ensure that window and door screens are intact and properly sealed to prevent adult flies from entering structures.