Bed bugs have been bothering humans for 60,000 years

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We humans might be the Earth’s apex predator, but it’s bugs that really rule the world. At least 5 million insect species live on our planet and some of them like to take up residence right alongside us. That includes bed bugs (Cimex lectularius). These pesky bugs have been thriving off of our blood for at least 60,000 years ago and may be considered our first “pest.”

According to a comparison of two recently sequenced whole genomes of two genetically distinct lineages of bed bugs, the human-associated lineage follows a similar movement pattern as our species and might be the first true urban pest. The findings are detailed in a study published May 28 in the journal Biology Letters.

The theory goes that about 60,000 years ago, a few intrepid bed bugs hopped off of a bat and clung to a Neanderthal walking out of a cave. The bugs from that lineage decided to see what tasty morsels our bipedal cousins could offer, while the other lineage stuck to bats. The decision to stick around with the hominids proved lucrative. They’ve been thriving ever since. However, the less adventurous bat-living bed bugs have seen their populations decline since the Last Glacial Maximum–aka ice age–about 20,000 years ago.

*A stairway graph (left) shows that the genome-wide patterns of bed bug (right) demography mirrors global human expansion. CREDIT: Block et al. 2025 and Warren Booth.*

This new study looked into the long lineage of these distinct bed bug populations. The two lineages have genetic differences, yet not enough to have evolved into two distinct species. Understanding the historical and evolutionary relationship between humans and bed bugs can help inform models that predict the spread of bugs and diseases as urban populations increase.

“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,” study co-author and Virginia Tech entomologist Lindsay Miles said in a statement.

Tying human expansion around the world to the emergence and evolution of urban pests like bed bugs can also help pinpoint the traits that co-evolved in both species.

“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. “The really exciting part is that the human-associated lineage did recover and their effective population increased.”

One of the instances includes early establishment of large human settlements that expanded into cities such as Mesopotamia roughly 12,000 years ago.

“That makes sense because modern humans moved out of caves about 60,000 years ago,” added study co-author and Virginia Tech entomologist Warren Booth. “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 the human population increased and living in communities and cities expanded, the human-associated lineage of bed bugs experienced an exponential growth in their effective population size.

[ Related: What head lice can tell us about human migration. ]

With the whole genome data in this study, the researchers now have a foundation for further study of this 245,000 year old lineage split in the bugs. The team is interested in focusing on the evolutionary changes 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.”

The team has already found a gene mutation that could contribute to that insecticide resistance they found in a separate study published in March that they will continue to examine for more clues. Understanding how that gene works could lead to solutions to handle these notoriously difficult to get rid of bugs.