Bedbugs lurk behind walls and in crevices. "They're so wafer-thin they can crawl into the smallest cracks, they're avid feeders, and they're as fast as greased lightning," says Dr. Dickson Despommier of Columbia University's Mailman School of Public Health. "But they essentially disappeared because of the overuse of DDT." The 1972 U.S. banning of DDT is one explanation for the insects' rebound. But, though the bugs are once again "a serious nuisance", Dr. Despommier doesn't see their reemergence as a public health crisis. "As far as we know," he says, "they don't have the capability of transmitting diseases. That's important to point out, because it's easy for people to overreact to these things."