Bed bugs split from their bat-loving ancestors when they joined early humans exiting caves 60,000 years ago.

While the bat bugs declined, the human-associated lineage exploded in urban settings, adapting and even developing pesticide resistance. Their story reveals just how closely pests can evolve alongside us.

Ancient Bed Bug Origins

Around 60,000 years ago, a few adventurous bed bugs made a bold move. They left their bat hosts behind and climbed onto Neanderthals emerging from caves. That decision changed everything. These pioneering pests began a long and thriving relationship with humans -- one that continues to this day.

Meanwhile, their bat-loving cousins weren't so lucky. Those that stayed behind have seen their populations steadily decline since the last ice age, also known as the Last Glacial Maximum, about 20,000 years ago.

Now, new research led by scientists at Virginia Tech reveals just how deeply bed bugs have been entangled with human history. By analyzing the entire genomes of both bat- and human-associated bed bugs, the team found striking differences. The lineage that moved in with humans has followed a demographic path that mirrors our own. In fact, it may be the very first true urban pest.

Their research was published today (May 28) in the scientific journal Biology Letters.

Tracing Bed Bug History

"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," said Lindsay Miles, lead author and postdoctoral fellow in the Department of Entomology.

According to the researchers, the historical and evolutionary symbiotic relationship between humans and bed bugs will inform models that predict the spread of pests and diseases under urban population expansion.

By directly tying human global expansion to the emergence and evolution of urban pests like bed bugs, researchers may identify the traits that co-evolved in both humans and pests during urban expansion.

How Cities Helped Bed Bugs Bounce Back

"Initially with both populations, we saw a general decline that is consistent with the Last Glacial Maximum; the bat-associated lineage never bounced back, and it is still decreasing in size," said Miles, an affiliate with the Fralin Life Sciences Institute. "The really exciting part is that the human-associated lineage did recover and their effective population increased."

Miles points to the early establishment of large human settlements that expanded into cities such as Mesopotamia about 12,000 years ago.

Genetic Legacy of Human Migration

"That makes sense because modern humans moved out of caves about 60,000 years ago," said Warren Booth, the Joseph R. and Mary W. Wilson Urban Entomology Associate Professor. "There were bed bugs living in the caves with these humans, and when they moved out they took a subset of the population with them so there's less genetic diversity in that human-associated lineage."

As humans increased their population size and continued living in communities and cities expanded, the human-associated lineage of the bed bugs saw an exponential growth in their effective population size.

A Genetic Fork: Urban Bugs vs. Wild Cousins

By using the whole genome data, the researchers now have a foundation for further study of this 245,000 year old lineage split. Since the two lineages have genetic differences yet not enough to have evolved into two distinct species, the researchers are interested in focusing on the evolutionary alterations of the human-associated lineage compared with the bat-associated lineage that have taken place more recently.

"What will be interesting is to look at what's happening in the last 100 to 120 years," said Booth. "Bed bugs were pretty common in the old world, but once DDT [dichloro-diphenyl-trichloroethane] was introduced for pest control, populations crashed. They were thought to have been essentially eradicated, but within five years they started reappearing and were resisting the pesticide."

Cracking the Genetic Code of Resistance

Booth, Miles, and graduate student Camille Block have already discovered a gene mutation that could contribute to that insecticide resistance in a previous study, and they are looking further into the genomic evolution of the bed bugs and relevance to the pest's insecticide resistance.

Booth said the project is a good example of what happens when researchers "follow the science," which he is afforded the space to do thanks in part to the Joseph R. and Mary W. Wilson endowment that supports his faculty position.

"It's a great resource to have," said Booth. "We are using it for work investigating the evolution of insecticide resistance and species spread using museum specimens collected from 120 years ago to our present-day samples. "I'm very lucky to have that freedom to explore."

Reference: "Were bed bugs the first urban pest insect? Genome-wide patterns of bed bug demography mirror global human expansion" by Lindsay S. Miles, Brian C. Verrelli, Richard Adams, Yannick Z. Francioli, Daren C. Card, Ondřej Balvin, Todd A. Castoe and Warren Booth, 30 April 2025, Biology Letters.

DOI: 10.1098/rsbl.2025.0061