Managing the Bugs That Cost You Money
External parasites cost the U.S. cattle industry billions of dollars annually through reduced weight gains, decreased milk production, hide damage, disease transmission, and treatment expenses. Unlike internal parasites that stay hidden, external parasites are often visible, but that does not make them easy to control.
Getting a handle on external parasites means knowing each pest's biology, seasonal patterns, and available control options. This guide covers the major external parasites affecting cattle and lays out practical strategies for keeping them in check.
Horn Flies
The Primary Economic Pest
Horn flies (Haematobia irritans) are the most economically significant external parasite of cattle in the United States. These small flies, about half the size of a house fly, spend almost their entire adult life on cattle and leave only briefly to lay eggs in fresh manure. They reduce weaning weights by 15-50 lbs per calf, decrease milk production (which further cuts calf growth), and are estimated to cause $1 billion in annual losses across the U.S.
Identification
Horn flies rest head-down on cattle and are typically found on the back, sides, and belly. Both males and females are blood feeders, taking 20-40 blood meals per day. The economic threshold sits around 200 flies per animal. Counts above that number justify treatment, and the estimate is straightforward: when flies are easily visible across the back and sides, you are likely past that threshold.
Life Cycle
The horn fly life cycle moves quickly. Females lay eggs in fresh manure pats, where larvae develop in 3-5 days. Pupae form in the soil under the manure pat and take another 3-5 days before adults emerge and seek a cattle host. Populations peak in summer, decline in fall, and overwinter as pupae in manure and soil.
Control Methods
Insecticidal ear tags are effective for 3-5 months. Apply them at the start of fly season and remove at the end to reduce resistance selection pressure.
| Tag Type | Active Ingredient Class | Duration |
|---|---|---|
| Organophosphate | Diazinon, pirimiphos-methyl | 3-4 months |
| Pyrethroid | Permethrin, cypermethrin, zeta-cypermethrin | 3-5 months |
| Macrocyclic lactone | Abamectin | 3-4 months |
| Combination | Multiple classes | 4-5 months |
Resistance Management
Horn fly resistance to insecticides is widespread. Rotate between insecticide classes on a multi-year cycle: use pyrethroid tags for a couple of years, then switch to organophosphate tags, then repeat. Signs of resistance include fly populations not dropping after treatment and the need for multiple treatments in a single season.
Face Flies
Disease Vectors
Face flies (Musca autumnalis) cluster around the eyes, nose, and mouth of cattle. While their feeding is less painful than horn flies, they are significant disease vectors that spread pinkeye (Moraxella bovis), IBR virus, and Thelazia (eyeworms).
Identification
Face flies are gray with dark stripes on the thorax. They are non-biting flies that feed on secretions, clustering around the face. Unlike horn flies, they leave cattle to lay eggs in fresh manure.
Control Challenges
Face flies are harder to control than horn flies for several reasons. They only stay on cattle part of the day, they feed on the face where treatments have limited reach, and they do not remain on treated surfaces long enough for good contact. The best options include face dusts and fly bullets, dust bags positioned to contact the face, fly masks (though these are labor intensive), and pour-ons (which provide limited face coverage).
Stable Flies
The Leg Biters
Stable flies (Stomoxys calcitrans) are painful biters that attack primarily the legs of cattle. Unlike horn flies, they spend minimal time on the animal itself. Their bites cause cattle to bunch together for protection, which leads to heat stress. They also interfere with grazing behavior and cause weight loss and reduced milk production.
Identification
Look for a distinctive checkerboard pattern on the abdomen and a prominent proboscis (biting mouthpart). Stable flies attack the legs, belly, and sides during brief feeding visits lasting only 3-4 minutes.
Breeding Sites
Unlike horn flies, stable flies breed in decomposing organic matter rather than fresh manure. Primary breeding sites include old hay and straw, silage edges, feed bunks with spilled feed, manure mixed with bedding, and wet decomposing vegetation.
Control Methods
Sanitation is the most effective strategy for stable flies because it addresses breeding sites directly. Clean feed bunks regularly, manage silage edges, and eliminate decaying vegetation near cattle. Chemical control with pour-ons and permethrin sprays provides some protection but requires repeated applications. Traps can help around confinement areas, though you need multiple traps to make a real dent in the population.
Cattle Lice
Winter Parasites
Lice are host-specific parasites that cause the most problems in winter months. Two types affect cattle. Chewing lice (Bovicola bovis is the most common) cause intense irritation and scratching. Sucking lice are more damaging than chewing lice and include several species: the long-nosed cattle louse (Linognathus vituli), short-nosed cattle louse (Haematopinus eurysternus), little blue cattle louse (Solenopotes capillatus), and cattle tail louse (Haematopinus quadripertusus).
Economic Impact
Lice infestations reduce weight gains by 0.25-0.5 lb per day, decrease feed efficiency, and cause hide damage. Heavy infestations of sucking lice can cause anemia, and animals often injure themselves from rubbing against fences and structures.
Seasonal Pattern
Lice populations build during winter when thicker hair coats provide protection and animals are in closer contact, especially in confinement. Populations peak between January and March. During summer, sunlight exposure and increased grooming behavior knock populations down, though lice may persist at low levels.
Identification
Watch for rough, patchy hair coats, hair loss from rubbing, raw or irritated skin, restlessness, and poor condition despite adequate nutrition. When checking for lice, examine the topline, neck, shoulders, and tail head. Chewing lice are fast-moving and yellow-brown in color, while sucking lice are slower and darker. You can also spot eggs (nits) attached to hair shafts.
Control Methods
Pour-on products applied along the backline spread through the hair coat and may be sufficient as a single treatment in mild cases. Treat the entire herd, since lice spread by contact. Injectable macrocyclic lactones are effective against sucking lice but less effective against chewing lice because they work systemically.
| Infestation Level | Treatment Protocol |
|---|---|
| Light | Single fall treatment |
| Moderate | Fall treatment, repeat in 2-3 weeks |
| Heavy | Treat, repeat in 14 days, treat again in 14 days |
Cattle Ticks
Species of Concern
Several tick species affect cattle, each with different geographic distributions and disease concerns. Gulf Coast ticks transmit Heartwater (if introduced) and cause "gotch ear," a swelling and damage to the ears. Lone Star ticks are aggressive biters with a multi-host life cycle that transmits ehrlichiosis and tularemia. American dog ticks transmit Rocky Mountain Spotted Fever and anaplasmosis. Rocky Mountain wood ticks transmit RMSF, Colorado tick fever, and anaplasmosis. Winter ticks can build large populations on cattle during their fall to early spring activity period.
Economic and Health Impact
Direct damage from ticks includes hide damage, secondary infections, stress, irritation, and reduced weight gains. The disease transmission threat is even more costly, with tick-borne diseases and the potential introduction of exotic diseases like cattle fever posing serious risks.
Life Cycles
Most cattle ticks follow a three-host life cycle. Larvae hatch from eggs on the ground and attach to small mammals, feed, drop off, and molt to nymphs. Nymphs feed on medium-sized mammals, drop off again, and molt to adults. Adults feed on cattle and other large mammals, then females drop off, lay eggs, and die. One-host ticks (like cattle fever ticks) can build large populations quickly because all stages occur on the same animal.
Control Methods
Pour-on products applied along the backline provide residual activity and should be repeated as needed based on tick pressure. Injectable macrocyclic lactones are not as effective as contact treatments, though they work better for some species than others. Ear tags are less effective for ticks than for flies but may help reduce ear tick damage. Sprays and dips give good coverage but are labor intensive. Environmental management through mowing tall grass and brush, rotational grazing, and wildlife management (deer harbor many tick species) can reduce overall tick pressure.
Tick Checks
Regular examination helps catch infestations early. Focus on the ears, tail head, brisket, under the front legs, and the perineal area.
Mange Mites
Types Affecting Cattle
Sarcoptic mange (Sarcoptes scabiei) is highly contagious, reportable in the U.S., and causes intense itching with crusty lesions. Psoroptic mange (Psoroptes ovis) is also reportable and produces large, spreading lesions with severe economic impact. Chorioptic mange (Chorioptes bovis) is usually mild with limited spread and most common in winter. Demodectic mange (Demodex bovis) is usually mild and causes nodules in the skin.
Identification
Signs of mange include hair loss in patches, crusty or scabby skin, thickened skin, and weight loss in severe cases. A skin scraping examined under a microscope is needed to confirm the diagnosis and identify the mite species.
Control
Treatment typically involves pour-on products, and multiple treatments are usually needed. Treat all animals that have been in contact with affected cattle.
Integrated Pest Management
Principles
Effective external parasite control combines multiple approaches:
- Monitoring to know what parasites you have and their population levels
- Thresholds to treat only when economically justified
- Multiple tactics rather than relying on a single approach
- Resistance management through rotating insecticide classes
- Sanitation to reduce breeding sites where possible
Seasonal Control Calendar
Spring: Treat for lice if still present, begin feed-through IGR if using it, and check for winter tick damage. Summer: Apply ear tags at the start of fly season, maintain dust bags and back rubbers, reapply pour-ons as needed, and manage stable fly breeding sites. Fall: Remove old ear tags, apply lice treatment with a one-time fall pour-on, and clean up fly breeding material. Winter: Retreat for lice if needed, check for chorioptic mange, and prepare for spring fly control.
Cost-Benefit Analysis
For horn flies, the economic threshold sits at 200 flies per animal. Losses above that threshold run $20-50 per head, while treatment costs $3-10 per head, so there is a clear economic benefit when the threshold is exceeded. Keep in mind that continuous treatment accelerates resistance over time, and integrated approaches reduce your dependence on any single chemical class.
Working with Your Veterinarian
When to Consult
Call your vet for unusual parasite problems, treatment failures, suspected mange (remember that sarcoptic and psoroptic mange are reportable diseases), heavy tick infestations, concerns about parasite-transmitted diseases, or help developing an integrated control program.
What Your Vet Can Provide
Your veterinarian can identify parasites, run disease testing, make treatment recommendations, access prescription products if needed, and share regional information on resistance patterns in your area.
Frequently Asked Questions
Bottom Line
Different parasites require fundamentally different approaches, so knowing exactly which pests you are dealing with is the first step in any control program. Seasonal patterns drive your treatment timing: lice peak in winter, flies build through summer, and ticks vary by species and region.
Rotating insecticide classes is essential for horn fly resistance management, and sanitation makes the biggest difference for stable fly control. When treating for lice, you need to hit the entire herd since individual treatment leaves a reservoir of reinfestation. Not every fly justifies reaching for a chemical, so use economic thresholds to guide your decisions. The most durable results come from an integrated approach that combines chemical tools, sanitation, monitoring, and management practices rather than relying on any single tactic.
Related Articles
- Internal Parasite Control Strategies
- Horn Fly Management Options
- Tick-Borne Disease Prevention
- Pasture Management for Parasite Control
References
- Byford, R.L., Craig, M.E., & Crosby, B.L. (1992). A review of ectoparasites and their effect on cattle production. Journal of Animal Science, 70(2), 597-602.
- Cortinas, R. & Jones, C.J. (2006). Ectoparasites of cattle and small ruminants. Veterinary Clinics of North America: Food Animal Practice, 22(3), 673-693.
- Taylor, D.B., Moon, R.D., & Mark, D.R. (2012). Economic impact of stable flies on beef cattle. Journal of Economic Entomology, 105(6), 1894-1901.
- Texas A&M AgriLife Extension. (2024). External Parasites of Cattle. Publication E-208.
- Drummond, R.O. (1987). Economic aspects of ectoparasites of cattle in North America. The Economic Impact of Parasitism in Cattle, 9-24.
- USDA-APHIS. (2024). Cattle Fever Tick Eradication Program Guidelines.
