When it comes to successful relationships, there’s nothing quite like the long, long marriage between bedbugs and humans, even if the affection goes in one direction.
The species of bedbug that feeds on us while we slumber is monogamous with humans; it does not shack up with any other species. Despite the ick factor, the insect does not transmit disease, nor does it cause harm beyond the mild irritation where its needlelike mouth pierces the skin.
That relationship, it turns out, has been going on for much longer than previously known.
According to a new study published in the journal Biology Letters, the bedbug’s long affair with humans began about 245,000 years ago. The insect strayed from the cave-dwelling bats that had been its sole source of sustenance and discovered the blood of a Neanderthal, or some other early human, that had bedded down in the same cave.
From that point on, scientists say, bedbugs diverged into two distinct species: one that lived off bat blood, and one that fed on humans.
“You’re not going to find a bedbug in your garden,” said Warren Booth, a professor of urban entomology at Virginia Tech and a lead author of the study. “They are completely reliant on us to spread.”
After a decline that accompanied early man’s nomadic existence, the human-dependent bedbug population began to explode about 13,000 years ago, the study found.
That surge coincided with humanity’s shift to sedentary living in Europe and the Middle East.
“When humans decided they liked being around other humans and started to build cities, the bedbug population skyrocketed,” said Lindsay Miles, an entomology researcher at Virginia Tech and an author of the study. “For bedbugs, it was a sweet deal.”
The findings, based on genomic analysis of the human-associated bedbug’s DNA to unlock its evolutionary past, help shed light on the relationships between people and pests that have long shaped human civilization. Sometimes the relationship can be deadly, as was the case with Bubonic plague, which killed millions when infected fleas jumped from rats to people.
The study suggests that the pairing between humans and bedbugs is thousands of years older than that with the German cockroach or the black rat, said Brian Verrelli, a biological data scientist at Virginia Commonwealth University who studies how human urbanization affects the natural world.
“These findings tell us something about how long and strong our marriage with the bedbug has been,” said Dr. Verrelli, who was also an author of the study. “It could have jumped off humans at any point, but it stuck around for the ride.”
Klaus Reinhardt, a bedbug researcher at the University of Tuebingen in Germany who was not involved in the study, said he was fascinated by what the study revealed about the genetic bottleneck that bedbugs had faced 40,000 years ago, when early humans traded cave life for nomadism and bedbug populations declined.
That bottleneck could have led to inbreeding and the loss of genetic diversity, but it did not appear to have had a negative impact on bedbugs. “As it turns out, they do very well with inbreeding,” Dr. Reinhardt said.
There are many things to admire about the bedbug. It can survive more than a year without feeding. It injects an anesthetic and anticoagulant to numb the human skin while feeding. And then there’s its unique mode of reproduction, “traumatic insemination,” which involves the male piercing the female’s abdomen to insert sperm directly into her body cavity.
For Dr. Booth of Virginia Tech, the bedbug’s most notable superpower is its ability to eventually overcome the pesticides used against it. It does this through rapid genetic mutation prompted by exposure to toxic chemicals, but also through the production of enzymes that can break down lethal compounds inside the bug’s body before they do damage.
This is what happened in the 1940s, when the widespread use of DDT led to a huge reduction in bedbug populations in the United States and other industrialized countries. At the time, some scientists hoped that humans had finally attained the divorce from bedbugs they had long sought.
But within a few years, Dr. Booth said, bedbugs had found a way to outsmart DDT. In the decades since, their populations have continued to surge, thanks to globalization, the rise of inexpensive air travel and accelerating urbanization.
Bedbugs excel at reproduction. A single pregnant female stowed away in a suitcase or hitched to a pant leg can produce 30,000 offspring in six months, all genetically related.
“Within two years, we’ve shown that one bedbug can infest multiple apartments in a multistory building,” Dr. Booth said.
In his two decades of studying bedbugs, Dr. Booth says that he has never had an infestation at home. The lab has strict protocols, and when traveling, he has been known to check behind hotel headboards and under mattresses.
“I don’t do that anymore,” he said, “because I always put my suitcase on the metal rack and then when I get home, everything goes in the washer.”
Andrew Jacobs is a Times reporter focused on how healthcare policy, politics and corporate interests affect people’s lives.
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