SEATTLE - Those mysterious bug bites that show up from time to time might be an indication of an unwanted guest in your home.

They could be the pest that the rat dragged in.

While King County Health worker Don Pace says he hasn't seen a growth in Seattle's rat population, investigators are seeing more "rat mites."

"This last spring as rat problems start building up in houses, rats start going out and foraging from there, we got a flood of calls in the spring," said Todd Murray, of the Washington State University Extension Office.

Non-native tropical rat mites are moving in. They live in the rat's nest and feed on them, but when the rat leaves or is trapped: "The mites need to go look for a new food source," Murray said. "They can't survive on humans as a food source but they bite into them."

The mite bites look like bug bites, and while they are irritating, they're otherwise harmless.

But, if Seattle's rat population is not growing, it would appear the mite population is.

Experts say the mites usually have to ride a rat into your home before they are a threat to you.

So you may not think the rats Don Pace kills in your sewer are a problem.

"I've dealing with about 20 right now active," he said.

And when Don talks about 20 complaints, he's talking about people who call the health department to say they've got a rat in their toilet. The mites can also get close to you by riding rats into your attic or crawl space.

But the good news is the mites won't stay long after the rat leaves, and so far they are not known to spread any diseases. But they are an invasive species and another rat problem that inspectors want to keep a lid on.

The best advice for avoiding rat mites is to avoid rats and keep them out of your home.

The following information on rat mites comes from the WSU Extension:

Biology

These small mites are 1-1.5 mm in length, grey to yellowish or even reddish after a blood meal.  Their normal hosts include Rats, mice, hamsters and probably other rodents as well.  While tropical, the rat mite can be a problem in temperate regions particularly where rats are allowed to flourish or when purchased rodents come home already infested.  Adult female tropical rat mites can live a couple of months and can lay about 100 eggs.  The average length of the life cycle is about 11 days.  When their normal hosts are killed, these mites will travel long distances often along pipes, wires in walls, or from branches of trees to the outside of homes.  Rat mites can survive extended periods without a meal so once the host (rat) problem has been solved; often rat mites can continue to be problematic and do not immediately leave.  They can remain on site up to two months after the rats are removed.  The bites of these mites are irritating and sometimes a painful condition will persist for several days, leaving red spots on the skin.  This is a condition that can be produced by several arthropods so if bitten be sure to submit specimens to an expert for positive identification because other creatures such as fowl mites, fleas, etc. can bite too.

Management Options

-Select Non-Chemical Options As Your First Choice!

- Determine if there is a rodent problem and if they are accessing the attic or crawl space or other points on the structure.

- Deny their access by vent screen repairs or making sure the screen vent mesh size is small enough that even mice cannot get through.

- Rats nesting in trees can be a problem also.  The branches that touch homes act as freeways for wandering mites which will access the house/ attic from such limbs.  The mites can wander relatively long distances in search of a host.  Branches touching homes should be trimmed back.

- Implement a rodent control program.  In some cases this is best achieved by a Pest Management Professional