Black flies (Simuliidae) are small, biting pests that can make outdoor activities unbearable, particularly near running water where they breed. Unlike common house flies, these insects seek a blood meal, which means standard food-based traps are ineffective for control. Creating a successful trap requires understanding the black fly’s unique host-seeking behavior and mimicking the signals it uses to locate a target. This article provides actionable, do-it-yourself strategies to construct traps that specifically target the female black fly.
Understanding Black Fly Behavior
Black flies are notoriously difficult to trap because their attraction is not based on sweet food or decaying matter. The female fly, which is the biting pest, is driven solely by the need for a blood meal to develop her eggs. Consequently, she is attuned to cues that signal the presence of a living host.
The primary attractant for a host-seeking black fly is carbon dioxide (CO2), which is exhaled by mammals and birds. This chemical signal, detected at long ranges, directs the fly toward a general area where a host may be present.
As the fly nears the source, other physical cues guide the final approach. Black flies have a strong visual preference for dark colors, such as black, dark blue, and brown, which contrast against the background. They also respond to heat and moisture, sensed at close range to confirm the target is a living body.
Simple Physical Trapping Methods
Effective black fly traps must use specific visual cues to lure the insects in for capture.
Dark Sticky Traps
One simple and low-cost method involves creating a dark-colored sticky trap. A sheet of dark plastic, especially black or dark blue, should be coated with a sticky substance such as petroleum jelly or a thick motor oil.
These dark-colored traps should be placed low to the ground near areas of high black fly activity. The dark surface visually mimics a host, and the flies that attempt to land will become instantly stuck.
Water Pan Traps
Another effective physical trap is a shallow water pan trap, enhanced with a dark color. By filling a dark-colored tray or pan with water and adding a few drops of dish detergent, you create a surface that is irresistible to the flies. The dark color attracts them visually, and the soap breaks the water’s surface tension. When the fly lands on the water, it sinks and drowns, trapping it effectively without the need for a sticky coating.
Enhancing Traps with Lures
To achieve high-volume trapping, physical traps must be enhanced with a chemical lure that mimics breath, specifically a source of CO2. A simple, low-cost CO2 generator can be created using a mixture of yeast, sugar, and water in a sealed container. This mixture ferments, continuously producing a plume of carbon dioxide that mimics a breathing host.
To construct this lure, combine two cups of sugar, one package (about 8 grams) of active dry yeast, and two quarts of lukewarm water in a sealed plastic bottle. The yeast consumes the sugar, converting it into alcohol and carbon dioxide gas, which then seeps out of the container. This fermentation process can last for two to three weeks, providing a steady supply of the primary black fly attractant.
The CO2 lure should be placed immediately adjacent to the physical trap. Positioning the entire setup downwind of the area you want to protect is important, as the CO2 plume will naturally drift with the air current, drawing flies from a wider range. Adding a piece of moist, dark cloth near the trap can further enhance its effectiveness by providing a secondary scent and moisture cue.