A network of caves in southern Oregon, thought to be among the earliest known sites of human habitation in the American West, turns out to have hosted other residents, too: bed bugs.

Archaeologists have found the remains of several species of bed bugs dating back as much as 11,000 years — the oldest ever found — revealing new insights into the distant relatives of the parasitic insects that infest modern mattresses.

The ancient bugs were found in the basalt rockshelters known as Paisley Caves, which have been an object of fascination since archaeologists first reported finding signs of human occupation — including fossilized human feces — said to be as much as 14,300 years old.

Some anthropologists have disputed these findings, but the caves remain the subject of intense study.

(Read about the debate surrounding the caves: “Ancient Feces From Oregon Cave Aren’t Human, Study Says, Adding to Debate on First Americans”)

Among the wealth of material found in the caves are thousands of bones belonging to long-extinct fauna, including mastodons, ancestral horses, and camels.

(Learn about the recent horse discovery from the caves: “Ice Age Cave Dwellers in Oregon Lived Among Extinct ‘Stout-Legged’ Horses, Fossils Show“)

It was amid these remains that two archaeologists searched for some evidence of the cave’s smallest animal inhabitants: insects.

Martin Adams, of the Portland-based firm Paleoinsect Research, and Dr. Dennis L. Jenkins of the University of Oregon’s Museum of Natural and Cultural History, sifted through the material from the site known as Cave 2 and found 14 specimens of bed bugs, most of which belonged to 3 different species.

Found in layers that have been dated to between 5,100 and 11,000 years old, they’re the oldest bed bugs — known to scientists as cimicids — ever reported.

However, Martin said in a press statement, these were “not the bed bugs we all know and love from hotel rooms.”

Instead, these kinds fed on bats.

There are two species of bed bugs that parasitize humans, the scientists explained: Cimex lectularius and Cimex hemipterus.

These insects are thought to have started out as bat parasites, but then adapted to eat human blood after humans began living in caves with infected bats.

By contrast, the three species discovered in Paisley Caves — Cimex pilosellus, Cimex latipennis, and Cimex antennatus — are distant cousins of those parasites, and none of them today are known to parasitize humans.

The find raises a number of questions for researchers about what life might have been like when humans occupied the caves at the end of the last Ice Age.

For example, one of the bed bug species is only known today in warmer regions, suggesting that the climate of southern Oregon was substantially warmer than it is now.

“The presence of warm-tolerant cimicids in the caves, such as Cimex antennatus, may suggest that climatic conditions at Paisley Caves 5,100 years ago were similar to what Cimex antennatus enjoys today in its current range,” Adams said.

But perhaps more importantly, the scientists want to know why the Paisley Caves bed bugs shared these caves with humans, but failed to fully make the transition to becoming human parasites.

Bat-specific species of bed bugs have been known to infest humans, the researchers said, and as they write in their report, “it is probable that similar occurrences befell the human occupants of Paisley Caves.”

But the experts are puzzled about why those bugs didn’t go on to remain human parasites, and spread throughout the ancient West on the bodies of the earliest Americans.

(Read about an important artifact found nearby: “Stone Tool Unearthed in Oregon ‘Hints’ at Oldest Human Occupation in Western U.S.“)

“Were the cimicid populations too small to establish themselves outside the caves, or were the host populations too small?” Adams asked, in his press statement.

“Given that Paisley Caves was only a seasonal occupation area for human hunter-gatherers, did the humans move around too much, or were the bugs not able to withstand the environment outside the caves for very long?

“Or, were there other constraints involved?

“I’m working on these last few archaeological questions right now.”

In any case, the scientists said, these tiny insect remains may yet produce big insights, given further study.

“Even if no intersection between man and bug occurred,” the pair writes in their report, “this assemblage is important, for it serves as the earliest record of the genus Cimex recorded to date.

“The Paisley Caves specimens not only have the potential to shed light on past cimicid distributions in the Pacific Northwest but also, with finer chronological resolution and wider spatial sampling, allow us to examine changes in the cimicid populations as both bat populations and environments at Paisley and surrounding rock shelter complexes changed over time.”

Adams and Jenkins report their findings in the Journal of Medical Entomology.