Fly paper is a common, low-tech method of pest control that relies on biological attraction and physical entrapment to manage flying insects. This simple device exploits the natural sensory biases of flies, luring them toward a sticky, non-drying surface. Manufacturers design these traps to incorporate specific visual and chemical signals that trick flies into approaching the paper.
Visual Cues and Fly Perception
Flies possess large compound eyes that perceive the world differently than human eyes, making certain colors and patterns highly attractive. Their visual system is particularly sensitive to shorter wavelengths of light, including the ultraviolet (UV) spectrum, which humans cannot see. This heightened UV sensitivity plays a role in how they perceive colors like blue and yellow, which are often used in fly paper design.
Historically, many fly papers were colored yellow because it was believed to mimic the color of new plant growth, a common food source for many flying insects. However, research suggests that for common house flies, the color blue, and particularly a specific shade of blue, is significantly more attractive, sometimes outperforming yellow by a factor of three or more. Blue is thought to attract flies because it balances ultraviolet light and shadow, which is highly stimulating to their compound eyes.
The presence of patterns on the paper also enhances its appeal by mimicking natural landing sites. Flies are naturally drawn to areas of high contrast, such as the edge of a surface or a dark crevice. Adding black lines or contrasting spots to the sticky surface exploits this behavior, providing a visual cue that suggests a safe resting spot or a food source.
Olfactory Attractants and Chemical Lures
While visual appeal is one mechanism, the use of scents provides a powerful, long-range signal to draw flies to the trap. Flies use specialized olfactory hairs on their antennae to detect volatile organic compounds (VOCs) in the air. These compounds guide them toward sources of food, mates, and suitable egg-laying sites. Modern fly papers incorporate chemical lures, often embedded directly into the adhesive, to exploit this acute sense of smell.
These chemical attractants are designed to mimic the odors flies naturally seek out, such as fermenting materials or decomposing organic matter. Specific compounds, like 1-octen-3-ol, which is present in meat, or 3-methylphenol, a component of chicken manure, have been shown to elicit a strong reaction in a fly’s olfactory cells. By using synthetic mixtures of these compounds, manufacturers can create an attractive “perfume” that is non-toxic and more stable than using actual decaying matter.
Some traps also use food-based scents that are sweet to simulate ripe or overripe fruit, or nitrogen-containing compounds that signal the presence of protein, which is necessary for adult flies’ sexual development. These pre-baited glues are effective even in areas that already have strong background smells.
The Mechanism of Capture
The final element of fly paper is the adhesive, which ensures that attraction results in capture. The sticky component is a carefully balanced formulation designed to remain perpetually tacky without drying out, even when exposed to air for long periods. This non-drying property is achieved through a blend of materials, including natural resins like rosin, synthetic polymers, and various oils or tackifiers.
The glue’s effectiveness is due to its high viscosity and cohesive strength, which create a physical barrier for the insect. When a fly lands, the adhesive immediately adheres to the tiny hairs and segments of its legs and body. Because the fly is lightweight and has a small surface area, the adhesive forces are much stronger than the fly’s ability to pull itself free.
Manufacturers fine-tune the adhesive’s tackiness to be strong enough to entrap the insect without being so viscous that it is difficult for users to handle or unroll the trap. The material is a type of pressure-sensitive adhesive, meaning the stickiness is activated upon contact, preventing the fly from gaining any traction to escape.