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Northern Fowl Mite Infestation

The Northern Fowl Mite (NFM) (Ornithonyssus sylviarum) is a relatively common ectoparasite of chickens. They are very small mites, ranging in size from 0.6-1 mm (0.02-0.04 in).
Northern fowl mites appearance
NFM permanently live their entire lives on their host, spending most of their time on the feathers, traveling to the skin surface to feed on blood. During heavy infestations, NFM can cause the chickens a great deal of stress, pain and blood loss (they can potentially lose 6% of their blood daily).

Clinical signs of Northern Fowl Mites

Chickens infested with NFM may appear very irritated, and be seen trying to scratch themselves by rubbing up against objects and biting at their feathers.
Signs of northern fowl mites in chickens
Feathers in the vent area may be soiled and blackened, due to the accumulation of dried blood and scabs, mite eggs, excrement, and cast skins. You may be able to see them moving in their feathers (as tiny dark specs). Using a bright flash light, inspect the chicken's feathers by parting them to see the skin, especially in the vent area.

How Northern Fowl Mites are Transmitted to Chickens

NFM are found on a wide range of domestic and wild birds, rodents, wildlife, and domestic animals. They can survive off their hosts for 2 to 3 weeks under optimal conditions.

Northern Fowl Mite Vs Red Poultry Mite

Northern fowl miteRed poultry mite
Adult Appearance  
Size0.5-1 mm (0.02-0.04 in)1-1.5 mm (0.04-0.06 in)
ColorGray to blackGray to black
Turns redYesYes
Body typeOvalOval
SpeedSlow movingSlow moving
Visible to the naked eyeAs tiny dark specsYes
Feeds onBloodBlood
Where they are foundVent, breast, and legs. Less commonly on the head and neck.Hide in crevices and cracks during the day, feed on chickens at night
TransmissionWild birds, rodents, contaminated equipment (fomites) and personnelWild birds, rodents, wildlife, dogs, cats, humans, contaminated equipment
Where eggs are laidWhite to off-white bundles of eggs found along the feather shaft of the vent.Lays eggs in cracks and crevices
Average Life cycle5-7 days2 weeks
How you can tellEarly infestations may be difficult to notice, but once numbers increase they can be clearly seen in the feathers and running along the skin surface. May also be seen on recently laid eggs.Look for them at night on the birds
TemperatureCool weatherWarm weather
Clinical signsDermatitis, poor condition (feathers appear 'dirty'), anemia, pale pink comb, soiled feathers near ventRestlessness at night, dermatitis, anemia, may cause chickens to alter where they roost at night.
Carry diseasesNoYes

Clinical Signs

Blackened vent feathers (which is caused by an accumulation of fowl mite feces, dead mites, and dried blood)
Poor quality and/or missing feathers near vent
Pale comb/wattles (anemia)
Increased preening
Frequent scratching/irritation
Mites crawling on eggs
Blood stains on eggs


  • History
  • Clinical signs
  • Physical exam
  • Skin scrapings

Reported Cases

  • Case 1: Northern fowl mites in a Chicken Northern fowl mites resulted in anemia and death of a 3-year-old backyard flock rooster. The entire body of the rooster was covered with pinpoint black mites at the feather base. Ref

  • Case 2: Northern fowl mites in a Chickens Haematophagous mites were collected from the vent region and plumage of chickens in six hobby flocks of ornamental breeds in Sweden, one of which included turkeys. Soiled vent skin and feathers, dermatitis, hyperkeratosis, skin necroses and ulcers were observed in 12 necropsied birds from two of the flocks. The mites were identified as the northern fowl mite Ornithonyssus sylviarum. This was supported by sequence analysis of a 642 bp region in the mitochondrial cytochrome oxidase subunit 1 (COI) gene (COI) in mites collected from five flocks, which showed 97–99% sequence similarity to O. sylviarum by blast analysis. Pairwise sequence comparisons revealed nucleotide variations in the range of 0–2.8%, whereas amino acid sequences were highly conserved. Ref

  • Case 3: Northern fowl mites in a Chickens Wild birds may be considered a possible source of parasitic mesostigmatid mites for poultry, but only few studies explored this hypothesis. In addition, there is very little information about the parasitic mites present in commercial poultry systems from southern South America. To contribute with data on parasitic mesostigmatid mites at the domestic-wildlife interface, we conducted a study in which samples were systematically collected from laying hens and wild birds (adults and nestlings), for two years at three commercial laying hen farms. The occurrence of mesostigmatid mites were compared among hosts. A proportion of the collected mites were morphologically identified to the species level, finding that host preference varied greatly depending on mite species: laying hens were only parasitized by Ornithonyssus sylviarum, wild bird nestlings were mostly parasitized by Ornithonyssus bursa, and in small proportion, by O. sylviarum, while adult passerines were parasitized by both Ornithonyssus species, and sporadically by Pellonyssus cf. reedi and Dermanyssus cf. triscutatus. In laying hens, there was intra- and inter-annual variability in mite occurrence, but no consistent seasonal pattern, whereas in adult wild birds, mites showed the highest prevalence in spring and the lowest in summer. Not coinciding with this general pattern, the occurrence of O. bursa matched the reproductive activity of wild birds. A phylogenetic analysis based on a fragment of the 16S rRNA gene was carried out for a subsample of the mites collected, showing that the O. sylviarum mites present on adult wild birds and laying hens had the same haplotype (100% identity). Additionally, mites obtained from wild birds morphologically identified as O. bursa presented two distinctive haplotypes (89.8% identity), one phylogenetically related to O. sylviarum and the other to O. monteiroi. These findings show that in central Argentina commercial laying hens are parasitized mainly by O. sylviarum while wild birds are also hosts to other mite species. Adult wild passerines, especially house sparrows, may be a source of O. sylviarum for commercial poultry. Ref

  • Case 4: Northern fowl mites in a Chickens Establishment and spread of Ornithonyssus sylviarum were documented through time on sentinel hens (50 per house of 28,000–30,000 hens) in the first egg production cycle of three large commercial flocks (12 houses) of white leghorn hens. Mites were controlled using acaricide, and the impacts of treatment on mite populations and economic performance were documented. Mite prevalence and intensity increased rapidly and in tandem for 4–8 weeks after infestation. Intensity declined due to immune system involvement, but prevalence remained high, and this would affect mite sampling plan use and development. Early treatment was more effective at controlling mites; 85% of light infestations were eliminated by a pesticide spray (Ravap), versus 24% of heavy infestations. Hens infested later developed lower peak mite intensities, and those mite populations declined more quickly than on hens infested earlier in life. Raw spatial association by distance indices (SADIE), incorporating both the intensity and distribution of mites within a house, were high from week-to-week within a hen house. Once adjusted spatially to reflect variable hen cohorts becoming infested asynchronously, this analysis showed the association index tended to rebound at intervals of 5–6 weeks after the hen immune system first suppressed them. Large, consistent mite differences in one flock (high vs. low infestation levels) showed the economic damage of mite parasitism (assessed by flock indexing) was very high in the initial stages of mite expansion. Unmitigated infestations overall reduced egg production (2.1–4.0%), individual egg weights (0.5–2.2%), and feed conversion efficiency (5.7%), causing a profit reduction of $0.07–0.10 per hen for a 10-week period. Asynchronous infestation patterns among pesticide-treated hens may have contributed to a lack of apparent flock-level economic effects later in the production cycle. Individual egg weights differed with mite loads periodically, but could be either higher or lower, depending on circumstances and interactions with hen weight. Individual hen weight gains were depressed by high/moderate mite loads, but the heavier hens in a flock harbored more mites. This led to compensatory weight gains after mites declined. Tradeoffs between resource allocation to body growth or production versus immune system function appeared to be operating during the early and most damaging mite infestation period, when high egg production was beginning and the hens were gaining weight. The results were related to other studies of mite impact on domestic hens and to wild bird–ectoparasite studies. Much of the mite economic damage probably is due to engaging and maintaining the immune response. Ref

  • Case 5: Northern fowl mites in a Pigeon Four pigeons which lived together of same cage were referred due to excessive feather loss, severe itching, and erythema on the head, neck and flank regions. They had behavioral problem with feather bloating and plucking. Although they were mildly depressed, appetite was normal. On microscopic examination of feather picking, prominent external parasite infection was found. Mite infection was diagnosed with morphological confirmation. On analysis of complete blood count (CBC), eosinophilia was evident. The patients were treated with ivermectin (apply 200 mcg/kg topically two times per every other week and spray 200 mcg/ml solution every week). Clinical signs of four, pigeons were improved 45 days following first therapy. This case report indicates that mite infection is accompanied with severe feather loss, itching, and generalized erythema on the skin and behavioral problem with feather bloating and plucking. And this infection can be managed with topical and spray application of Ivermectin without injection. Ref

  • Case 6: Northern fowl mites in a Chickens The mean body weight of White Leghorn roosters was approximately 100g less than that of uninfested roosters 4 weeks after they were infested with the northern fowl mite, Ornithonyssus sylviarum. Both groups increased in weight throughout the 20 weeks of the test, but the differences in weight remained. Reproductive potential studies showed that after moderate populations of mites (101-1000 mites/rooster) were observed, the volume of seminal fluid decreased. Four weeks before the test ended, one-half of the infested roosters produced an average of less than 0.1 ml. of seminal fluid per week while the other half showed a decrease of 0.07 ml. in volume of seminal fluid produced when compared with the control. Sperm concentration of mite-infested roosters increased as the volume of seminal fluid decreased but was not significantly different from the controls. Motility and live/dead ratios of sperm did not show significant differences. Serum testosterone levels were significantly decreased by mite populations. Hematology studies showed the greatest decrease in red blood cell counts, and packed cell volume occurred from the 4th to the 8th week when infestations were initially increasing rapidly. Mean hemoglobin concentrations for the infested birds were numerically lower but not significantly different from the controls. No specific anemia could be attributed to mite populations as all hematological values were within normal ranges. Ref


Spinosad (Trade name Elector PSP)Applied as a spray on all coop housing components.B Mullens et al., 2017; A Murillo et al., 2017; Dow AgroSciences 2001
Fluralaner (trade name Exzolt)Added to the flock's drinking water. The product is administered twice, 7 days apart so it treats two mite life cycles. There is no egg withdrawal period and trials show it to be 99% effective at killing mites.N Hinkle, et al 2018; A Prohaczik et al., 2017; B Mullens et al., 2017
Ivermectin0.2 mg/kg PO, SC, IM, topical once and repeated in 10-14 days.B Speer; W Campbell et al., 1984; S Lee et al., 2006
Garlic spray10% garlic solution diluted with water, sprayed on the chicken's vent and abdomen, once every 7 days for 3 weeks.Birrenkott, G. P., et al., 2000
Diatomaceous Earth (DE) (food grade)Apply by dusting onto the chicken's feathers or added to their dust bathing area. Also dust all housing components. Replace bedding and nesting material.A Murillo et al., 2016; C Martin et al., 2012; D Bennett et al., 2011, G Damerow
SulfurApplied as a dust directly on the chickens or added to their dust bathing area. Dust all housing components in coopA Murillo et al., 2016, G Damerow
MalathionUsed as a spray or powder applied to all housing components in coop.G Damerow
Carbaryl syntheticApplied as a powder (5% carbaryl) or spray (4 ounces of 80% carbaryl mixed in a 5 gallon bucket of water) directly on the chickens as well as all housing components. Replace bedding and nesting material.G Damerow
PyrethrumApplied as a powder or a spray on both the chickens as well as all housing components. Bedding and nesting materials should be replaced. When treating the bird, apply directly on the chicken's feathers, concentrating on the vent area. Note that it only kills the adult insects, not the larvae and eggs. Therefore, treatment will need to be repeated.G Damerow
PermethrinApplied as a powder (0.24% permethrin) or spray (3 ounces of 10% permethrin is mixed in a 5 gallon bucket of water), directly on the chickens as well as all housing components. Replace bedding and nesting material.G Damerow



  • Don’t trim beaks. It interferes with a chicken’s ability to self-groom.
  • Quarantine any new birds before adding to your flock.
  • Discourage wild birds by removing bird feeders and bird baths.
  • Control rodent populations, as they can sometimes be carriers of mites and ticks.
  • Provide your flock with an appropriate area to dustbath.
  • Thoroughly clean any branches, wood stumps, or other tree-sourced items containing bark.

Scientific References

Good Overviews

Age Range

Mites are more commonly found on 4 to 10 month old birds, after they reach sexual maturity.

Risk Factors

  • Cooler weather, less than 80°F (26.6°C)
  • Trimming beaks
  • Rodents on the premises
  • Contact with wild birds
  • Poor biosecurity procedures.