Bedbugs Could Have Been the First Urban Pest to Plague Human Cities, New Study Suggests
Scientists examined the genomes of two bedbug lineages to trace how their population sizes have changed over time
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The invention of cities could be to blame for the proliferation of bedbugs (Cimex lectularius), according to a new study. The paper, published Wednesday in the journal Biology Letters, suggests the insect might be the first true urban pest.
Bedbugs originally evolved more than 100 million years ago. At first, the parasites fed on an unknown host, and eventually, they moved to bat blood. But at one point around 245,000 years ago, some bedbugs made the leap to feeding on early humans—and they never looked back.
From there, the insects evolved in two lineages: the one that fed primarily on bats and the one that fed on humans. While both belong to the same species, the lineages have genetic differences. The research team set out to study their genomes.
They conducted a genetic analysis of 19 bedbugs from the Czech Republic. Ten of them came from the bat-feeding lineage, and nine came from the lineage that feeds on humans. The team estimated the bedbugs’ numbers over time by examining genetic mutations and modeling how large a population would have to be to create them, reports Science’s Rodrigo Pérez Ortega.
“We wanted to look at changes in effective population size, which is the number of breeding individuals that are contributing to the next generation, because that can tell you what’s been happening in their past,” says Lindsay Miles, a postdoctoral fellow at Virginia Tech and lead author of the study, in a statement.
During the last ice age, both lineages’ populations were in decline. But the human-feeding insects’ numbers began to rise around 13,000 years ago, the study found, which corresponds with the shift from nomadic to sedentary lifestyles about 12,000 years ago. Then, as large cities like Sumer in modern-day Iraq began to form around 7,000 years before the present, their numbers ticked up once again. The bat-feeding bedbugs, on the other hand, have continued to decline.
“Something different happened with human-associated bedbugs that caused that increase,” says study co-author Warren Booth, an entomologist at Virginia Tech, to Jake Buehler at Science News.
That timeline could mean bedbugs are the earliest urban pests, write the authors of the study.
“When we started to live in cities, we brought all these people together, and they all had their own bedbugs with them,” Booth explains to Ian Sample at the Guardian. “And then, as civilization spread across the world, the bugs spread with them to the point where they’re now ubiquitous in human society.”
Other pest creatures have lived alongside humans for millennia—such as the German cockroach and the black rat—but those animals appeared in urban regions more recently, within the last 5,000 years, according to the paper.
Some scientists are hesitant to call bedbugs the first urban pest, however. Michael Siva-Jothy, an entomologist at the University of Sheffield in England who was not involved in the study, tells the Guardian that another contender for the title could be head lice, which have been around for more than one million years. He also notes that the study only looks at a small number of bedbugs from one country.
Veera Singham, an urban entomologist at the University of Science Malaysia, tells Science that “the hypothesis is very compelling,” but that he would also like to see similar analyses of other pests, like fleas or lice. Still, regarding bedbugs, he adds, “I would agree, definitely, that they are one of the earliest.”
Follicle mites, which are tiny parasites that can only survive on human skin, are also contenders for the title, as Coby Schal, an urban entomologist at North Carolina State University, tells Science. There have yet to be any studies of their population over time.
“We’re splitting hairs a little bit, but I generally agree that [bedbugs] are the first, well-documented true pest of human-built structures,” Schal adds. “It’s a very solid paper.”
Booth says in a statement that the next step for the researchers could be looking more closely at their development during the last 100 to 120 years. “Bedbugs were pretty common in the old world, but once DDT [dichloro-diphenyl-trichloroethane] was introduced for pest control, populations crashed,” he says. “They were thought to have been essentially eradicated, but within five years, they started reappearing and were resisting the pesticide.”
Understanding how bedbugs continue to thrive could help create better ways to control them, the scientists suggest. Maybe then, we can stop worrying about bringing the pesky insects home.
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