Northern Fowl Mite: The Deadly Threat to Chickens

The northern fowl mite (Ornithonyssus sylviarum) is one of the most dangerous external parasites that can affect backyard chickens. Although tiny, these bloodsucking mites can rapidly overwhelm a flock, leading to anaemia, poor health and, in severe cases, death. If you’re a poultry keeper in the UK, understanding how to spot, treat and prevent these mites is crucial to keeping your hens safe and healthy.

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Why northern fowl mites are so dangerous

Northern fowl mites are incredibly small — much smaller than red mites — and difficult to detect in small numbers. However, their short life cycle makes them alarmingly fast breeders. A single mite can produce thousands of offspring in just a few weeks, and under ideal conditions (around 17°C or 65°F), a population can grow to over 20,000 mites within 70 days.

Unlike red mites, which tend to live in the coop and feed at night, northern fowl mites spend their entire lives on the chicken, feeding constantly. This round-the-clock feeding causes:

• Rapid blood loss and anaemia
• Weight loss and lethargy
• Pale comb and wattles
• A drop in egg production
• Increased vulnerability to other infections

If left untreated, a severely infested hen can die within weeks.

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How to spot northern fowl mite infestations

Because the mites are so small, early detection is difficult. However, in larger numbers, they become more obvious. Here’s what to look for:

• Greasy, clumped feathers, especially around the vent area
• Discolouration of the skin and feather bases due to mite faeces, eggs and dead skin
• Feathers that appear wet, matted or flattened, especially in damp weather
• Irritation or frequent preening
• Visible mites or tiny black specks crawling on the skin near the vent

Regular weekly checks, especially in colder months, are essential. Northern fowl mites are most active in cool weather and outbreaks are common in autumn and winter.

Tip: If you suspect mites and they crawl onto your hands or clothing, wash thoroughly and change before handling other birds.

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How to treat northern fowl mites

If your hens are showing signs of infestation, prompt action is vital. Treatment depends on the severity.

For mild to moderate infestations:

• Use a pyrethrum-based poultry dust or spray on the bird, focusing on the vent, underwings and base of the neck
• Apply food-grade diatomaceous earth (DE) to affected areas and the coop
• Repeat treatment after 5–7 days to catch newly hatched mites

For severe infestations or if hens are anaemic:

• Seek immediate veterinary advice
• Your vet may prescribe a more effective topical or systemic treatment
• Infected birds should be isolated from the rest of the flock until fully treated
• Monitor weight, appetite and egg production closely

Note: Mites have developed resistance to some over-the-counter treatments. If symptoms persist, professional intervention is recommended.

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Preventing northern fowl mite infestations

Prevention is far easier than cure. Good husbandry is key:

1. Routine inspections

Check your flock weekly for early signs of mites, especially around the vent area.

2. Dust bathing areas

Provide a clean, dry dust bath with diatomaceous earth to help hens stay mite-free.

3. Treat the environment

• Dust the coop, perches, nesting boxes and run with DE
• Clean and disinfect regularly
• Wash feeders and waterers frequently

4. Avoid reinfestation

Mites don’t usually leave the host, but a few can fall off and remain in the environment. Always:

• Isolate affected birds
• Treat all hens in the flock if one bird is infested
• Repeat treatment to break the life cycle
• Clean bedding and dispose of it offsite

5. Control wild birds and rodents

Mites can arrive on sparrows, pigeons or rats.

• Use vermin-proof feed containers
• Fence off or mesh any open areas
• Keep spilt feed cleaned up
• Consider an enclosed run if wild birds are common

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Final thoughts

Northern fowl mites are persistent, fast-breeding parasites that can severely harm your flock if not dealt with quickly. By checking your hens regularly, maintaining good coop hygiene and acting fast at the first signs of infestation, you can protect your chickens from this serious threat.

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Disclaimer

This article is for informational purposes only and does not constitute veterinary advice. If you suspect a severe mite infestation or your chickens appear unwell, consult a qualified poultry vet for diagnosis and treatment.