"Good night, sleep tight. Don't let the bedbugs bite" is a cheery little rhyme, but bedbugs are no joke if you have them. After decades of decreasing numbers, they're making a comeback — in clean homes and dirty homes and any homes they happen to reach.

"We're absolutely seeing more in Utah," says Diane Keay, environmental health area supervisor in the Salt Lake Valley Health Department.

Many experts believe the numbers declined because for many years people used broad-spectrum insecticides against household pests such as cockroaches. Bedbug control was a happy side effect. These days, people use specific insecticides against cockroaches, usually a bait the roaches carry back into the wall and share with others. But it's not a meal that attracts bedbugs, Keay says.

Rather, they're out for blood.

Bedbugs are not considered a public health crisis. They don't transmit any known disease so they're at the bottom of the list of issues that public health departments tackle. They're basically the responsibility of the homeowner or the landlord, Keay says.

That doesn't mean they can't make life miserable for people who have them in their home.

The bedbug that bites people, Cimex lectularius, is only about a quarter-inch long and is flat until it feeds. It's wingless and has a sharp beak to pierce skin. As it feeds, it injects a fluid that helps it get blood, and that's what makes skin swell and itch.

Cornell University's fact sheet says bedbugs usually bite at night, but if the light's low during the day, you're sitting still and they're hungry, all bets are off.

To reproduce, a bedbug drops as many as 50 eggs in crevices of bed frames, baseboards, floors and walls, among other sites. They hatch in six to 28 days, depending on room temperature. Once hatched, they feed as soon as they find a host. That's you. There can be as many as three generations a year, so they can take root and become an infestation quickly.

Getting rid of them, Keay says, requires a proactive approach.

She recommends vacuuming a lot. Although they're not associated with poor housekeeping, as some people have suggested, "none of us vacuum around the bed every day." You must, if you want to eradicate them without chemicals. And they're not just in the bed. They can be in carpets and wall baseboards and other places nearby. Be aware, as well, that they may settle in or around a favorite chair or hitch a ride in the fold of the backpack that's so often on you.

"They're coming to where there's going to be a warm meal on a regular basis, and they will not go further than they need to to hide," she says.