Bedbugs have rebounded worldwide over the last few decades. Developed countries had beaten back the infestations through the post-World War II use of DDT, but the discontinuation of that chemical has since given bedbugs the opportunity to adapt and colonize bedrooms globally. But how they spread so quickly from place to place – their pathway to new feasts of human blood – has never been well understood.

Now a team from the University of Sheffield has experimentally demonstrated one fast-track for bedbug infestation: in the folds of dirty laundry, as they show in the journal Scientific Reports this week.

“Soiled clothing left in an open suitcase, or left on the floor, of an infested room is likely to attract bed bugs,” write the biologists who conducted the experiments. “When packed into the suitcase, they will accompany their host back home.”

The human scent stays in the dirty laundry, and those organic compounds entice the blood-sucking pests, previous studies have shown.

The clothing traps traces of that body scent – and also draws in the bedbugs.

The experiments involved two rooms, one of which at any time was infused with carbon dioxide (which boosts the insects’ drive to seek out a host, like it does for mosquitoes).

A group of volunteers wore white socks and T-shirts for most of a day, and they were placed in two tote bags in each of the rooms about a meter away from two bags containing clean versions of the garments.

The bedbugs were given a meal of human blood 24 hours prior to being placed in the “arenas” for observation.

In between trial runs, the rooms were scrubbed with bleach and aired out thoroughly.

The bed bugs were allowed to travel through the “arenas.”

Ultimately, the bloodsuckers consistently tracked out the more pungent clothing, the final results show.

“Bed bugs were twice as likely to aggregate on bags containing soiled clothes compared to bags containing clean clothes,” they conclude.

The carbon dioxide-filled room consistently showed more activity from the parasites – demonstrating that they were spurred to seek out their blood feasts.

One way to combat the spread of bedbugs, said lead scientist William Hentley of Sheffield, is to limit the exposure of dirty laundry to the tiny tormentors.

“Our study suggests that keeping dirty laundry in a sealed bag, particularly when staying in a hotel, could reduce the chances of people taking bedbugs home with them, which may reduce the spread of infestations,” Hentley said.

Bedbugs have been tormenting humanity for all of modern history. Earlier this year, a study published in the Journal of Medical Entomology reported that evidence from an Oregon cave shows that the parasites from the genus Cimex made a jump from species of bats to humans at least as early as 11,000 years ago.