Flies locate necessary resources by detecting minute traces of chemical signals in the air. This highly developed sense of smell, known as chemoreception, guides them to sources of food, water, and appropriate sites for laying eggs. Flies rely on a volatile chemical signature to determine if a location offers the sustenance they need or the high-protein environment their offspring require. Understanding the specific compounds that attract flies is key to managing their presence.
How Flies Sense Chemical Signals
Flies detect airborne chemical messages using specialized sensory organs on their antennae. These organs are covered in tiny, hair-like structures called sensilla, which house the olfactory receptor neurons. Volatile organic compounds (VOCs) that evaporate from potential sources enter the sensilla and bind to specific receptor proteins.
This binding process converts the chemical signal into an electrical impulse that travels to the fly’s central nervous system. The brain quickly processes the unique combination of activated receptors, allowing the fly to interpret the odor’s meaning instantly. This rapid interpretation triggers an immediate behavioral response, directing the fly toward the attractive scent.
Compounds Signaling Protein and Waste
For many species, especially house flies and blowflies, the most powerful attractants are compounds released during the breakdown of protein-rich organic matter and animal waste. These scents signal an ideal nursery for their larvae, which require a high-protein diet to mature. The decomposition process, initiated by bacteria, generates a complex plume of VOCs that acts as a strong olfactory beacon for female flies.
The most recognizable scents of decay are the biogenic amines, putrescine and cadaverine. Putrescine is a product of the amino acid ornithine’s breakdown, while cadaverine results from the decomposition of lysine. These two diamines are responsible for the pungent odor associated with rotting flesh and serve as a primary signal for carrion-feeding flies.
Additional compounds enhance this attraction, including sulfur-containing gases like dimethyl disulfide and dimethyl trisulfide, which are also released as protein material decomposes. Waste products, such as urine and feces, release ammonia as they break down, a byproduct of nitrogen and protein metabolism. Ammonia intensifies the site’s attractiveness, indicating a high concentration of nitrogenous material suitable for larval development.
Attractive Volatiles from Sugars and Fermentation
Flies that seek energy and sustenance, such as fruit flies and some house flies, are strongly attracted to the sweet, slightly acidic scents of ripening or fermenting plant material. These chemical signals reliably indicate a source of readily available sugars and carbohydrates. The volatile profile of overripe fruit or spilled sugary liquids is a potent combination of alcohols, acids, and esters.
A common and highly attractive compound is acetic acid, the primary component of vinegar, produced when bacteria convert ethanol into acid. The presence of ethanol, or alcohol, is another strong attractant, as it is a direct byproduct of yeast metabolizing sugars during fermentation. Flies are drawn to ethanol because it signifies a plentiful and easily digestible energy source.
The attraction is strongest when these compounds are combined, as studies show that acetic acid and ethanol are synergistically more effective than either chemical alone. Various esters, which are organic compounds responsible for sweet, fruity aromas, are released as fruit softens and begins to ferment. Esters, such as ethyl acetate, signal a high-value food source that is ripe and ready for consumption.
Applying Attractant Knowledge for Control
The knowledge of these distinct chemical attractants is applied directly in developing effective fly management strategies. Since flies are drawn to two major categories of volatiles—decay and fermentation—control methods target these specific signatures. Understanding the intense attraction to protein breakdown products means that sanitation is the most effective deterrent for house flies and blowflies.
Promptly removing pet waste, cleaning up food spills, and properly disposing of garbage eliminates the sources of putrescine, cadaverine, and ammonia that attract breeding flies. Conversely, fruit flies are highly sensitive to fermentation byproducts like acetic acid and ethanol, which is used to create targeted traps. Simple devices using a lure of vinegar or overripe fruit reliably draw in flies seeking those specific sugar-signaling compounds.
Commercial fly traps often utilize a combination of nitrogen-containing compounds and fermentation volatiles to create a broad-spectrum attractant for multiple fly species. By eliminating the source of the scent that signals a suitable egg-laying site or food source, homeowners can effectively break the fly’s reproductive cycle and reduce the overall population.