Mites Biting?

Advice for the Home Gardener from the Help Desk of the
UC Master Gardener Program of Contra Costa County

rat mite (ornithonyssus bacoti)
rat mite (ornithonyssus bacoti)
Client's Request:  Thank you for bringing the unknown biting insect to the UC Master Gardener Program Help Desk.

Help Desk Response:   As I said in our conversation today, your insect is not a bed bug, but rather a mite of some kind. From its appearance, I believe it is a rat mite. There are also bird mites that can invade homes and bite people, but its appearance is closer to the rat mite. 

These mites need rodents to survive, but will come into homes when their preferred hosts die or decrease in number. They cannot survive for too long without their hosts, even though they feed on humans. If there is a large population of rodents (rats or mice) in your attic or crawlspace, you might see a continued presence of these mites. 

Here is a link to information from Contra Costa Vector Control District: and from
Alameda County Vector Control about biting mites:

I didn't ask if you had rodent problems in your home, but I would be surprised if you did not (rat infestations are very common in our area). These links below are to information about controlling rats and mice:;
More information can also be found on the Vector Control districts.

I hope this information is helpful and you're able to get rid of these pesky biting creatures. Please let us know if you have more questions.

Help Desk of the UC Master Gardener Program of Contra Costa County (SEH)

Note:  UC Master Gardeners Program of Contra Costa's Help Desk is available almost year-round to answer your gardening questions.  Except for a few holidays (e.g., last 2 weeks December), we're open every week, Monday through Thursday for walk-ins from 9:00 am to Noon at 2380 Bisso Lane, Concord, CA 94520. We can also be reached via telephone:  (925) 608-6683, email:, or on the web at MGCC Blogs can be found at You can also subscribe to the Blog.



By Steve I Morse
Author - Contra Costa County Master Gardener