Fly paper is a common insect control tool. Understanding what draws flies to these traps reveals insights into their biology and sensory perception.
The Allure of Fly Paper
Fly paper utilizes substances that mimic resources for flies, drawing them in. Manufacturers incorporate attractants like sugars (sucrose, honey, molasses) and fruit extracts to simulate decaying fruit. These sweet compounds serve as energy sources, appealing to flies. Some formulations also include putrescent egg solids or yeast, generating odors associated with decaying organic matter.
Flies, particularly females, are driven to find suitable egg-laying sites, making decomposition odors attractive. Compounds like trimethylamine (from rotting fish) and indole (from fecal odors) are attractants because they signal breeding grounds. Certain fly papers may also contain pheromones, such as (Z)-9-Tricosene, a female fly pheromone to attract male flies. This combination of food-mimicking and breeding-site cues appeals to different fly species.
How Flies Detect the Lure
Flies possess specialized sensory organs to detect attractants from a distance. Their primary sense for locating food and breeding sites is olfaction (smell). Flies use their antennae, covered in sensilla (fine hairs), to detect volatile chemical compounds. Olfactory receptor neurons within these sensilla send electrical signals to the fly’s brain upon binding with odorant molecules.
A fly’s olfactory system is sophisticated, allowing it to discriminate hundreds of odorants. While some olfactory cells react to various smells, others are specialized to detect specific chemical signals. In addition to smell, flies rely on their compound eyes to locate the paper once close. Their eyes, composed of thousands of ommatidia, provide a wide, almost 360-degree field of vision, albeit with low resolution. Flies detect motion well and are attracted to bright colors, especially yellow, often used in fly paper design.
The Sticky Trap: Beyond Attraction
Once attracted, the physical trapping mechanism of fly paper ensures capture. The paper is coated with a specialized adhesive designed to remain sticky without drying. This non-drying property maintains effectiveness even when exposed to air and environmental factors. Common adhesive components include natural resins like rosin, vegetable oils, and waxes, sometimes combined with castor oil or sodium silicate.
The adhesive’s tackiness ensnares flies on contact. When a fly lands, its legs or wings become instantly stuck, preventing escape. The glue’s consistency is viscous enough to hold the insect firmly, even as it struggles. While attractants draw flies to the paper, the persistent, non-toxic stickiness of the adhesive ultimately secures them.