How much do you know about bird mites? Here, two academics from Sydney’s Westmead Hospital explain all about them, with advice on how best to control them. 

Bird mites belong to a group of arthropods that are morphologically very similar in appearance, yet have very different habits and ecologies. Failure to properly identify the mites to the species level can lead to incorrect treatments and non-control of the pest. If you are at all unsure, mites should be referred to an expert laboratory for proper identification, such as the Department of Medical Entomology, ICPMR.

Natural history

‘Bird mites’, ‘Tropical fowl mites’ or ‘Starling mites’ are the common names used to describe the mite Ornithonyssus bursa from the family of mites Macronyssidae. These mites (main picture, above) are often incorrectly called ‘bird lice’. Bird mites are most active during spring and early summer.

Ornithonyssus bursa is a small but extremely mobile mite, barely visible to the eye, with eight legs (except the larva that has six), oval in shape and with a sparse covering of short hairs. Bird mites are semi-transparent in colour, which makes them difficult to detect on skin until blood is ingested and then digested; when they may appear reddish to blackish.

The mite is widely distributed throughout warmer regions of the world. It is a parasite, feeding on the blood of common birds including pigeons, starlings, sparrows, Indian mynahs, poultry and some wild birds.

Contact with humans usually occurs after birds gain entry to roof cavities via broken tiles or through the unprotected eaves, of homes, factories, barns and other dwellings to construct their nests in early spring or summer. However, some infestations also occur from birds roosting on the outside of dwellings such as window ledges or awnings. The mites feed on the unfeathered nestlings, as well as the adult birds, and the large amount of nesting material used by the birds provide the mites with an ideal environment in which to thrive. The mites have a short life cycle (approximately seven days) and can rapidly generate large populations.

When the young birds leave the nest or die, many mites (often many tens of thousands) are left behind in the absence of a suitable host, and these will disperse from the nest into and throughout the dwelling searching for new hosts. Most mites will die within three weeks without a blood meal from a bird host. However, they will bite humans they encounter, although they cannot survive on humans.

Clinical presentation

As a result of their ‘test biting’ while searching for a new bird host, the mites inject saliva. Although bird mites are not associated with the transmission of any infectious disease, the bites can lead to severe irritation with rashes and intense itching. Scratching of the bites may result in secondary infections. The bites are often difficult to diagnose and can be mistaken for bites from a number of other arthropods.

The greatest impacts from bird mites are usually experienced in rooms close to the point of entry of the mites. The mites have no preference for any particular areas of the body and they do not live underneath the skin, nor can an infestation be maintained on humans. However,
the problem will persist while the bird-related source of the mites remains. Until the infestation is controlled, the occupants of the building can experience considerable discomfort. Also, the sensation of crawling mites on the skin will irritate some people.

Laboratory diagnosis

Identification by high-power light microscopy, using appropriate taxonomic keys, by an expert is the only method of correctly identifying the mite. Although Ornithonyssus bursa is the most common mite associated with infestation of homes there are several other mites associated with birds within Australia that can invade dwellings and bite humans.

These bird mites include Ornithonyssus sylviarum (northern fowl mite) and Dermanyssus gallinae (chicken mite). Also, a closely related species, Ornithonyssus bacoti (tropical rat mite), occasionally attacks humans. This species is associated with rodents, such as rats and mice, and their nests. Ornithonyssus bursa and Ornithonyssus bacoti are taxonomically very similar and are extremely difficult to differentiate.

Correct identification is absolutely necessary if appropriate control procedures are to be recommended.

Treatment and control

The irritation associated with bites can be alleviated with an anti-pruritic such as crotamiton (e.g. Eurax), but there is no specific treatment. Severe reactions may have to be treated as for other allergic conditions with antihistamines.

Unless steps are taken to control the mite infestation, symptoms resulting from bird mite bites will continue.

Once the mite has been correctly identified, appropriate steps must be taken to locate and remove the source/s of the infestation and prevent its recurrence. All nesting sites should be located and nesting material removed.

An insecticidal spray with a product labeled for bird mites can be applied to ensure total eradication of mites, but treatment of rooms without removal of nests in roof cavities will not stop further mites entering and the problem will continue.

Broken tiles or timber allowing access to roof cavities should be repaired and all potential entry points to the eaves and roof cavity blocked. Roosting and nesting sites on window ledges should be cleared and made unsuitable for future bird use.

Confirmation and enquiries

Identification of mites and all other medically important arthropods is performed through the Medical Entomology Department at ICPMR, Westmead Hospital. The Medical Entomology Department is the only NATA accredited laboratory in Australia for the identification of arthropods of medical importance.

Information on pest birds.

Merilyn Geary and Stephen DoggettDepartment of Medical Entomology, Westmead Hospital, NSW