Rat Mites

During May, the District received several calls and requests for service regarding rat mites.  Rat mites are ectoparasites that live in rodent nests and feed on their blood. These mites require rat blood to survive, but if rats have been recently eradicated from a home or the infestation is large, they will also bite people out of desperation. The most common rat mite San Mateo County is Ornithonyssus bacoti, the tropical rate mite, but there are several other species. Most people have an itchy allergic reaction to the bites, although not everyone in the same household may react similarly.


Ornithonyssus bacoti, the tropical rate mite, from a service request in May.

The best way to prevent rat mite bites is to keep rats from entering and nesting within a residence. If rats do become a problem indoors, they should be managed as soon as possible. Residents of San Mateo County can request an inspection from District technicians for no charge to detect any entry points rodents could use to access their homes. The technician will also give recommendations of how to seal up any openings or control an existing problem. If a house has an established rat infestation, often hiring a private pest control company is the best way to ensure successful eradication. Once the rodents are completely eliminated, mite activity will typically cease within a month.

Residents who suspect they are being bitten by rat mites can place sticky insect glue traps in the areas of their home that they suspect mites are biting them and bring them to the District. If itching from mite bites is causing distress, a pest control company can perform an acaricide treatment to reduce mite activity while the rat control is ongoing. Those who prefer not to have pesticides used inside their homes can endure mite bites with the help of topical corticosteroid creams and oral antihistamines, until the rat control work is completed and the mites die off on their own.