Bedbugs!

Of course, the best offense is a strong defense, and there are simple steps you can take to lessen the likelihood of infestation:

1) Plug the holes: "It's like looking at an English muffin," says Dr. Despommier. "These bugs seek out nooks and crannies in the environment, so prevent them from having breeding sites such as cracks, loose wallpaper, thousands of pictures on the wall. Just get a little bit handy with a spackling palette and some caulking products."

2) Clear the clutter: You don't have to be a packrat to be an unwitting bedbug collaborator—as Dr. Sorkin points out, "even screw holes in furniture" offer crevices where the critters can congregate.

3) Don't invite the little bastards in: "If you're staying in a hotel, ask for a vacuum cleaner to vacuum out your suitcase," Meek says. "When you get home, don't take your time unpacking; put the laundry immediately into the wash. And if possible don't store the suitcase in the living space." Also, beware those street-side finds: one person's treasure could be another's discarded infestation.