While bed bugs have been tormenting humanity for millennia, it’s long been assumed their evolutionary journey as parasites first began tens of millions of years ago, when they fed on bats. But an international team of scientists has found evidence suggesting the origin of these vampiric insects extends even further into the past — back to the heyday of dinosaurs.
When people think about bed bugs, they’re probably thinking about the common bed bug, or Cimex lectularius. But there are actually over 100 known insect species closely related to our bed bug, falling under the umbrella of the Cimicidae family.
These bugs, broadly known as cimicids, all need to feed on the blood of a host. Most species can really only survive off a single host species, but some can choose between a roster of fleshy eateries.
The leading theory is that the very first ancient bed bugs colonised ancient bats. That would put the start of their evolutionary branch, at most, sometime around 50 million to 60 million years ago. But the authors of this current study, published Thursday in Current Biology, say they’ve collected enough evidence that suggests a much older provenance.
Their case includes a genetic analysis of existing bed bug species that feed on birds and bats from a wide variety of bed bug sub-groups, scrounged up over a 15-year-span from caves and museums, as well as fossil evidence of an ancient cimicid-like insect that was preserved in amber more than 100 million years ago (its discovery was documented in 2002).
This fossilised insect probably isn’t the direct ancestor of cimicids today, but its close genetic relationship to the family helped the authors work out a timeline for the ancestral insect that would give rise to the bed bug.
Based on all of this evidence, they estimated this proto-bed bug first appeared sometime around 122 million years ago, with the lineage that would directly lead to bed bugs emerging sometime around 100 million years ago. This far predates the currently assumed origin of bats, and places them right in the Cretaceous period.
According to Warren Booth, a molecular ecologist at the University of Tulsa who studies bed bug evolution but is unaffiliated with this research, the team’s case is robust. And if they’re right, then bed bugs would be one of the most astonishing success stories this planet has ever seen.
“So put more easily, the asteroid that hit the Earth leading to the mass extinction event (known as the K-Pg mass extinction), was around 66 million years ago. So, bed bugs are older than that, and they lived through it. But, let’s go back further… T. rex appeared on the Earth around 77 million years, So, bed bugs were on this Earth before T. rex evolved,” Booth told Gizmodo via email. “To me, that is a pretty remarkable image.”
Funny as the idea of T. rex straining to scratch its bed bug bites would be, dinosaurs probably never hosted these ancient bed bugs, the authors noted. Even if dinosaurs were warm-blooded, as today’s bed bug hosts all are, they’re not thought to have lived or slept in any one place for too long. Bed bugs are terrifying, sure, but they’re also slow-moving and need a home base near their prey to make a living.
Aside from moving the starting point of bed bug evolution back, the authors say their findings may also overturn other common assumptions about the bed bug.
They found evidence, for instance, that bed bug species have rarely evolved from an incarnation that infested many types of animals to one that sticks to a single host. Evolutionarily speaking, it’s thought that parasites tend to switch from a wide array of hosts to a single one because it’s more resource-efficient. But that doesn’t seem to be true for bed bugs.
More often than not, bed bugs just switched from one single host to another, such as from birds to bats. Since most bed bugs today have specialised hosts, it’s unlikely that ancient bed bugs were any different, the authors said. But it’s still unclear what that animal might have been if it wasn’t bats.
“What that was is pure speculation, but to me, I think some of the arboreal ancestral birds, or possibly some of the arboreal mammal-like creatures [could be a possibility]” Booth said. “Will we ever know what the true ancestral host was? That’s unlikely, but we now know that it lived before T. rex, and that’s pretty amazing.”
Human-biting bed bugs seem to be an exception to this general rule, though. According to the authors, all three species that plague us evolved from bed bugs that used to only feed on a single host, but today these bugs can still feed on the blood of other animals (namely bats) if the opportunity presents itself. The findings also appear to throw a wrench into another theory about our personal history with bed bugs.
The bed bug species that feed on humans likely split off into their own branches quite a while before modern humans arrived (somewhere up to 2 million years ago). In other words, the bugs that now call us dinner already existed by the time we started living in caves and near bats—they just chomped onto a good opportunity when they saw it.
That said, while the common bed bugs that feed on us are genetically similar to their cousins that still live in caves or attics and mainly feed on bats, and can even interbreed in the lab, the two groups are slowly evolving away from one another.
“Ultimately, this is a very intriguing story that completely upends our understanding of the evolution of this lineage,” Booth said.
More than anything else, the findings highlight just how resilient bed bugs have been. Even human ingenuity hasn’t knocked the common bed bug down for long. The pesticides we developed in the mid-20th century nearly wiped them out, but they’ve staged a global comeback in recent decades, thanks to mutations that made them almost impervious to these chemicals.
And while the authors say their research should help us learn how to better manage these pests, it’s tough to imagine that they won’t find a way to bounce back from anything we throw at them.
After all, if a dino-killing asteroid apocalypse couldn’t stop their ancestors, what hope do we have?