Every pest manager will have received a call from a concerned customer about being bitten by ‘invisible’ insects. Sometimes these calls turn out to be a case of delusionary parasitosis, where the customer believes they are being bitten but no pests are present. However, it is important for the pest manager to assume that a pest is indeed present and to carry out an inspection accordingly. Whilst finding the common culprits for delivering bites in the home is relatively easy – namely fleas, bed bugs and lice – it is important to inspect for ‘invisible’ pests: mites.

Dust mites are a cause of allergic reactions but they don’t bite. Bird mites certainly do bite so could be a potential culprit. But an often overlooked candidate is the rodent mite. So what do you know about rodent mites?

The rodent mite or tropical rat mite (Ornithonyssus bacoti) is found Australia-wide and indeed in most countries globally, wherever there are rodents. Being a mite, it is not an insect, but belongs to the class of Arachnida. Varying in size between 0.75-1.5 mm long and pale grey in colour, they are somewhat transparent unless they have recently had a blood meal (as pictured above). Their size and colour make them very difficult to spot – the use of sticky traps, double-sided sticky tape and a hand-held lens are recommended to confirm their presence. However, distinguishing between bird mites and rodent mites is generally a job for experts. For a pest manager on the job, confirming identification is probably quicker by inspecting for rodent or bird activity in the building.

Pest managers may be somewhat familiar with bird mites, namely the tropical bird mite, Ornithonyssus bursa and the red poultry mite, Dermanyssus gallinae. Bird mites generally only become a problem when birds leave their nests in the roof void and the hungry mites invade homes in search of a blood meal. Although they will bite humans, they cannot actually continue their life cycle on a human host. The same cannot be said for rodent mites. Although they prefer rodents as a host, they will feed off other small mammals and humans when food is scarce.

Female adult mites drop off their host once they have had their blood meal and will lay up to 100 eggs. The eggs hatch within 1-2 days and the whole life cycle can be completed in 7-16 days. The bites are typically small, red raised areas 1-4 mm in diameter, often in a cluster and can be anywhere on the body. The inflammatory reaction is caused by their saliva and the itching and inflammation can last for several weeks. However, as with any potential bite, diagnosis should be carried out by a medical professional, not a pest manager! Although rodent mites have been shown to be capable of transmitting a variety of diseases, such as murine typhus, in the laboratory, this has not been confirmed in the field.

As rat mites can travel up to a hundred metres on their own (without hitching a ride on a rodent) and can survive extended periods without feeding, treating a rodent mite infestation needs to be thorough. Assuming it is indeed a rodent mite rather than bird mite, the first step is to find and treat any rodent problems in and around the property. Infested rooms should be thoroughly vacuumed before being treated with an appropriate residual insecticide. The contents of the vacuum container should be placed in a sealed bag and placed in the garbage. Treating furnishings and mattresses with a suitably labelled insecticide may also be necessary and the use of mattress protectors can be considered. Fogging with an appropriately labelled product is an alternative to spraying surfaces, depending on the situation. If the rodent nest can be located the nesting material should be removed (whilst wearing gloves and a mask) and the surrounding areas should also be treated with an insecticide.

So if your customer is complaining about being bitten and an obvious culprit cannot be identified, take some time to inspect and set up traps to see if rodent mites are present.

More information on rodents.