Horse flies are certainly worse this year because a mix of warm weather, wet conditions, and changes in local habitats have created perfect breeding grounds. This article explores the five main reasons for horse fly surge we are seeing now. We will look at the science behind the horse fly infestation severity and give you tips for controlling excessive horse flies.
Grasping the Horse Fly Life Cycle
Horse flies (family Tabanidae) are more than just an annoyance. Their bites are painful because the female fly uses blade-like mouthparts to slash the skin and lap up the blood pool. This feeding style leads to high levels of irritation and can transmit diseases. To truly address why are biting flies worse now, we must look at their life cycle.
The life cycle has four stages: egg, larva, pupa, and adult.
- Eggs: Females lay hundreds of eggs, often near moist soil or standing water.
- Larvae: These live in mud, decaying vegetation, or water. They eat small insects or organic matter.
- Pupae: This resting stage occurs in moist soil.
- Adults: This is the biting stage. Females need blood meals to develop their eggs.
Anything that favors moist, warm soil environments will lead to increased horse fly activity.
5 Key Reasons for the Horse Fly Surge This Year
Several interconnected environmental factors are contributing to the horse fly population boom we are experiencing. These are the five biggest factors affecting horse fly populations right now.
1. Unusually Warm and Extended Spring Weather
Warmth speeds up development. Horse flies are highly sensitive to temperature. When spring starts early and stays warm longer than usual, it pushes the entire population cycle ahead.
Faster Development Times
Warmer soil temperatures mean larvae hatch sooner. They also reach the pupal stage faster. This shortens the time it takes for a new generation of biting adults to emerge.
- Shorter larval development period.
- More generations can occur in one season.
- This directly increases the overall horse fly biting frequency.
If the weather stays warm well into the traditional ‘fly season,’ we get overlapping broods, making the problem feel constant rather than cyclical. This is a primary reason for horse fly surge.
2. Excessive Rainfall and Moisture Levels
Moisture is critical for the early life stages of horse flies. The larval stage requires damp soil, mud, or aquatic environments to survive.
Ideal Larval Habitats
Areas that were dry in previous years might have seen lower fly numbers. However, heavy spring rains or sustained wet periods create perfect mud flats and saturated edges around ponds or ditches.
- Increased Mud: Muddy areas near livestock watering troughs become nursery grounds.
- Flooding Runoff: Water pooling in low-lying fields provides temporary habitats for larvae.
This abundance of wet habitat supports a larger number of larvae reaching adulthood, leading to a higher horse fly infestation severity. When managing severe horse fly problems, controlling water runoff becomes vital.
3. Changes in Local Land Management Practices
How we manage land directly impacts where flies breed and thrive. Recent changes in land use can favor the flies.
Reduced Grazing Pressure or Overcrowding
If fields are rested longer (less grazing), vegetation grows thicker. This thick grass traps moisture near the ground. This damp, sheltered environment protects developing larvae from drying out or from predators.
Conversely, if animals are crowded into smaller, wet areas for extended periods (like sacrifice paddocks during wet springs), they churn the soil into perfect fly breeding mud. Both scenarios can contribute to bad horse fly season causes.
Altered Water Features
Draining wetlands or, conversely, letting small ponds become stagnant and overgrown can affect the balance. While too much water is bad, stagnant, nutrient-rich water also supports the fly larvae that live near the edges.
4. Decline in Natural Predators
Every insect has predators. If the populations of natural enemies decline, the horse flies have fewer checks on their numbers.
Bird Populations
Birds like swallows and flycatchers eat adult horse flies. A drop in these predator bird populations means more flies survive to bite and lay eggs.
Beneficial Insects in the Soil
The larval stage in the soil is eaten by ground beetles and certain wasps. If soil health is poor, or if broad-spectrum pesticides were used in previous years, these beneficial predators might be reduced. Fewer predators mean a larger horse fly population boom. This is a key component of why controlling excessive horse flies is so difficult year over year.
5. Warmer Winters Leading to Higher Overwintering Survival
The adult flies themselves do not usually survive harsh winters, but the developing stages—especially the larvae deep in the soil—are susceptible to hard freezes.
Milder Winters Increase Survival Rates
If winters are milder, with fewer deep or sustained freezes, more larvae survive underground. They are primed to emerge early in the spring as soon as temperatures rise, giving them a significant head start on the season. This early emergence contributes heavily to the perception of increased horse fly activity right from the start of the warm season.
Assessing the Severity: Is This Year Truly Worse?
Many people feel the flies are worse, and the data often supports this feeling. We can gauge the horse fly infestation severity by looking at a few key indicators related to biting behavior and population density.
Measuring Increased Horse Fly Activity
It’s not just about the number of flies you see; it’s about how aggressively they bite.
- Bite Rates: Monitoring the average number of bites an animal receives per minute provides a baseline. A sharp increase over previous years indicates a surge.
- Flight Period Extension: If flies are active weeks earlier or later than usual, it indicates a longer season, which translates to more cumulative biting events.
- Area Density: Are the flies present in areas where they were scarce before? For example, are they now heavily populating shaded woodsides instead of just open pastures?
Table 1: Factors Contributing to High Biting Frequency
| Environmental Factor | Impact on Larvae/Pupae | Impact on Adult Flies | Result |
|---|---|---|---|
| High Spring Temps | Faster development | Earlier emergence | Increased horse fly biting frequency |
| Prolonged Wet Soil | High survival rate in mud | Successful transition to adulthood | Higher population density |
| Mild Winters | More larvae survive underground | Larger starting pool | Greater horse fly infestation severity |
The Link to Climate Change
Experts note that bad horse fly season causes are increasingly tied to broader climate patterns. As average global temperatures rise, the geographical range of many insect pests, including horse flies, expands northward or to higher elevations. This means areas previously too cool for major outbreaks are now experiencing them.
Strategies for Managing Severe Horse Fly Problems
When you face managing severe horse fly problems, a single solution rarely works. Integrated Pest Management (IPM) is necessary, focusing on breaking the life cycle at multiple points. These steps help reduce the horse fly population boom.
Targeting the Larval Stage (The Most Effective Point)
Because larvae are so tied to moisture, controlling damp soil is key to controlling excessive horse flies.
Water Management
- Drainage: Improve field drainage to eliminate standing water and overly saturated soil in pastures, especially near feeding stations or gates where animals congregate.
- Mud Reduction: Use heavy gravel or wood chips in areas that always turn to mud (like entrances or near water troughs) to dry the top layer of soil. This makes the environment unsuitable for larvae.
Biological Controls (Limited Use)
Some research explores using parasitic nematodes or fungi that attack fly larvae in the soil. However, these are complex to apply correctly and may not be effective against the horse fly infestation severity seen in a major outbreak year.
Targeting the Adult Stage (Reducing Biting)
Adult flies cause the immediate pain and stress. Controlling excessive horse flies means addressing the adults that are currently flying.
Traps
Large-scale trapping can reduce local populations. The most common effective trap mimics a host animal.
- CO2 Traps: These traps release carbon dioxide, heat, and moisture, mimicking a breathing animal. Horse flies are strongly attracted to this plume.
- Janse or Horse Fly Traps: These often use a dark, inflated ball (mimicking a rear end) over which the flies land, only to be funneled into a collection container. They are highly effective for reducing horse fly biting frequency in small areas.
Repellents and Barriers
For immediate relief for horses and livestock:
- Topical Sprays: Look for pyrethrin-based sprays. They offer short-term protection but must be reapplied often, especially after rain.
- Fly Sheets and Masks: Physical barriers are essential. UV-protective fly sheets cover most of the body, preventing the female fly from landing and slashing the skin. This is crucial for managing severe horse fly problems on sensitive animals.
Environmental Control
Reducing harborage areas around barns and resting spots helps. Clear away heavy, damp leaf litter or dense, low vegetation where flies rest during the hottest parts of the day.
Why Are Biting Flies Worse Now? Specifics on Impact
The combination of warm, wet springs and mild winters directly answers why are biting flies worse now. It is a compounded effect leading to higher numbers and longer activity.
Impact on Animal Health and Welfare
High horse fly biting frequency is not just an annoyance; it’s a health issue.
- Stress and Weight Loss: Animals stressed by constant attacks spend less time eating and more time swatting or running. This leads to lower weight gain, especially in young stock.
- Disease Transmission: Horse flies are mechanical vectors for diseases like Equine Infectious Anemia (EIA). Higher fly numbers mean higher risk of transmission.
- Secondary Infections: The deep cuts made by horse flies can become infected, requiring veterinary care.
Interpreting Local Weather Data
To predict if you will face bad horse fly season causes next year, look at the data from this year:
- Did the soil temperature rise above 60°F (15.5°C) consistently before May 1st? (Indicates early larval development.)
- Did the region experience more than 120% of its average spring rainfall? (Indicates ideal larval habitat.)
- Did the winter see fewer than five consecutive days below 10°F (-12°C)? (Indicates high overwintering survival.)
Answering yes to these points strongly suggests that increased horse fly activity is inevitable.
Final Thoughts on Controlling Excessive Horse Flies
The horse fly population boom this year is driven by perfect environmental synergy: warmth speeding things up and moisture providing the nursery. Effective controlling excessive horse flies requires a multi-pronged approach focused heavily on managing damp ground where the larvae thrive. By disrupting the breeding cycle through drainage and habitat modification, you can lessen the horse fly infestation severity for next season, even if the weather remains favorable for these persistent pests.
Frequently Asked Questions (FAQ)
Q: Are horse flies attracted to dark colors?
A: Yes, female horse flies are highly attracted to large, dark, moving objects, as these mimic the silhouette of large grazing animals. Using lighter-colored fly sheets can sometimes reduce initial attraction compared to black or dark blue.
Q: How long does a typical horse fly season last once it starts?
A: The active adult season usually lasts from late spring through late summer (June to August/September). However, due to warmer weather, the season is often starting earlier and ending later, extending the period of increased horse fly activity.
Q: Do repellents work on horse flies as well as mosquitoes?
A: Some ingredients, like DEET or Picaridin, offer limited repellent action against horse flies. However, pyrethrins offer better knockdown protection when the fly lands. Physical barriers (fly sheets) are generally far more reliable for managing severe horse fly problems than sprays alone.
Q: Can I eliminate horse flies from my property entirely?
A: Complete elimination is nearly impossible because they travel, and their larval stages are deep in the soil. The goal of controlling excessive horse flies is to reduce the population to a manageable level where animal stress and health risks are minimized.