March flies (tabanids or horse flies) present a persistent challenge during the warmer months. These insects are notorious for their painful bites, delivered by the female seeking a blood meal necessary for egg production. Eliminating a March fly problem requires a comprehensive, multi-pronged strategy that addresses both immediate protection and long-term population reduction.
Identifying the March Fly Nuisance
March flies are typically stout-bodied insects ranging from 6 to 25 millimeters, often featuring large, prominent eyes. The females are the ones that bite, using strong, piercing mouthparts to lacerate the skin and extract blood. This process is distinctly painful compared to a mosquito bite. Males are harmless and feed only on plant nectar and juices.
These flies are visual hunters, actively seeking out hosts during daylight hours, particularly on warm, calm, and sunny days. They are attracted to dark colors and large, solid shapes, which they mistake for potential hosts. Understanding this visual cue is a foundation for both personal protection and successful trapping efforts.
Adult flies are generally most abundant in the spring and early summer, but activity continues throughout the warmer season. Their life cycle, from egg to adult, can take many months or even years, depending on the species and environmental conditions. Once they emerge, adult flies typically live for about three to four weeks.
Personal Protection and Repellent Strategies
Immediate protection requires a combination of physical barriers and chemical deterrence. An effective defense is to wear long, light-colored, and loose-fitting clothing when outdoors, which physically blocks access to the skin. March flies are specifically attracted to dark colors, particularly dark blue, so avoiding these hues makes you a less appealing target.
Chemical repellents offer an additional layer of safety against these persistent biters. The most reliable products contain active ingredients such as diethyltoluamide (DEET), picaridin, or Oil of Lemon Eucalyptus (OLE/PMD). Repellents in a lotion or gel formulation are often considered the most effective application method for March flies.
The product must be applied evenly to all exposed skin surfaces and reapplied according to the manufacturer’s directions, especially after swimming or heavy sweating. For children, apply the repellent to the carer’s hands first and then spread it onto the child’s exposed skin, avoiding their eyes and mouth. Natural or organic repellents exist, but they are generally not as effective as those containing the primary active ingredients.
Active Control and Trapping Solutions
Large-scale insecticide spraying for adult March flies is typically ineffective because they are highly mobile and their breeding sites are extensive and difficult to locate. For localized control around homes or properties, specialized traps are the most practical solution for reducing adult populations. These traps exploit the fly’s strong visual attraction to dark, moving objects and heat.
Effective traps often feature a large, dark-colored object, such as a black rubber ball or bucket, suspended in a sunny area. The dark object absorbs solar energy and radiates heat, simulating the target animal’s body heat and attracting the flies. As the flies approach, they are guided upwards into a collecting chamber or onto a sticky surface.
One common design involves a dark-colored box or board, approximately 60 cm square, coated with a permanently sticky adhesive. Commercial traps, such as the H-trap, use a similar principle, incorporating a dark ball under a funnel to direct the flies into a container. Placing these traps strategically in open, sunny areas where fly activity is high can significantly reduce the number of biting females locally.
Habitat Modification for Population Reduction
Long-term management focuses on disrupting the March fly life cycle by targeting their breeding grounds. Larvae develop in moist environments, including damp soil, rotting vegetation, sand, and rot holes in trees. Since the life cycle is slow, eliminating these breeding sites now will affect future generations.
Managing standing water and improving drainage in boggy areas is a foundational step in habitat modification. March fly larvae require consistently moist substrate to survive and develop. Removing or managing accumulations of organic waste, such as decaying leaf litter and manure, reduces the food source and habitat for the developing larvae.
In agricultural or livestock settings, careful manure management is especially important for population control. By proactively drying out or removing potential larval habitats, property owners can limit the emergence of adult flies over time. Since the flies can travel long distances from their breeding sites, this strategy is most effective when applied broadly across a community or region.