Flypaper is a simple, low-tech method of insect control used for over a century to manage flying pests like house flies. Unlike chemical sprays or electric zappers, it functions by purely physical means, relying on a specially formulated adhesive to immobilize insects upon contact. Its effectiveness stems from a combination of chemistry, physics, and insect biology, which together counteract a fly’s natural ability to cling and detach from surfaces.
The Composition of the Sticky Substance
The adhesive coating on flypaper is a non-drying glue engineered to maintain its tackiness and viscosity over extended periods. It is typically composed of a blend of natural resins, such as rosin, combined with high-viscosity oils like castor oil or petroleum-based oils. This formulation prevents the glue from hardening or evaporating, a common issue with other adhesives.
Resins and polymers provide the necessary cohesive strength, while the oils act as non-volatile solvents, ensuring the sticky surface remains pliable and active. Some commercial formulations may also include ingredients like polyisobutylene or butyl rubber to enhance durability and flexibility. This composition ensures the adhesive layer is tacky enough to form an immediate bond with an insect yet remains fluid enough to resist the insect’s attempts to pull itself free.
The Physical Mechanism of Trapping
A fly’s ability to walk on surfaces relies on its legs, which are equipped with tarsal pads (pulvilli) that secrete a thin, oily emulsion for adhesion. To release its grip, a fly performs a controlled “peeling” action, lifting the pad edge-first to minimize the force required for detachment. The flypaper’s high-viscosity glue defeats this escape technique by immediately adhering to a large surface area of the insect’s body or legs.
When an insect lands, the viscous glue flows around the minute structures on its feet, drastically increasing the contact area. This physical entanglement overwhelms the fly’s limited muscle power, preventing it from executing the localized peeling motion. The fly is forced to attempt to pull its entire foot straight off the surface simultaneously, requiring a force far greater than its small body can generate. The resistance of the thick, sticky substance quickly exhausts the insect, leaving it permanently trapped.
Attractants: Luring the Target
The paper itself acts as an active lure designed to draw flies toward the adhesive surface. Many commercial flypapers utilize visual cues, most commonly a bright yellow color, which is highly appealing to many flying insects. The yellow hue mimics the appearance of certain plant foliage or flowers, prompting the insects to land and explore.
Chemical attractants are embedded within or coated onto the adhesive, complementing the visual attraction. These may include simple sugars, molasses, or more complex compounds like pheromones or specific food-based scents. For instance, the pheromone Z-9-tricosene (Muscalure) is often added to mimic the scent of female house flies, drawing males to the trap. This combination of visual and chemical signals increases the probability that a fly will make the initial contact necessary for the physical trapping mechanism to take effect.