Ancient Insect Discoveries From Across Colorado (Part 1)

In the first part of a two-part series, we look at a 50-million-year-old katydid fossil with intact organs, a 49-million-year-old cockroach fossil that rewrites its evolutionary history, and hundreds of Folsom era weevil abdomens from an undescribed species.

Katydid (Green River Formation)

Katydid Fossil from Green River Formation in Rio Blanco County, Colorado
Katydid fossil from Green River Formation | Paleontological Association

Layers of sedimentary rocks formed by intermountain lakes that existed 50 million years ago make up the fossil-rich Green River Formation. This Eocene formation extends from northwestern Colorado to northeastern Utah and southwestern Wyoming. Existing for an incredible 12 million years before drying up, the Green River Lake System was one of the oldest on Earth. It left behind one of the greatest accumulations of lake sediments ever recorded.


From within the sedimentary layers, archaeologists made the exciting discovery of a fossilized katydid, an “assassin bug” species rarely seen in the fossil record. According to palaeoentomologist Sam Heads, katydid fossils are so rare, “any new katydid fossil you find represents a new data point in the evolutionary history of katydids.” The Green River katydid fossil, measuring only half an inch in length, was no exception.


When viewing the fossil under a microscope, researchers were amazed to find that not only had the hard structures of the 50-million-year-old katydid specimen been preserved, so had the insect’s internal organs. Visible in the fossil were segments of its digestive canal, muscle fiber traces, and other delicate tissues. Rarely seen in sediment-buried fossils, these soft structures allowed researchers to learn a great deal about how katydids evolved over time.

A katydid hanging from a leaf
Modern Katydid | Haneesh K.M.

The age of the fossil was significant as well. It allowed researchers to determine the katydid branch of the “assassin bug” family was 25 million years older than previously thought. Furthermore, they learned the species developed its distinct leafy appearance and supersensitive hearing much earlier in its evolutionary history than believed.

Cockroach (Green River Formation)

Fossil from the Eocene Green River Formation
Ectobius fossil from Green River Formation | Smithsonian Museum of Natural History

Another significant insect fossil discovered at the Green River Formation was a 49-million-year-old cockroach belonging to the Ectobius genus. Researchers previously believed this species of cockroach originated in Europe and Africa around 44 million years ago. Discovery of the Green River cockroach allowed them to determine the Ectobius genus traces its beginnings to North America, not the Old World, and appeared on Earth 5 million years earlier than believed.

Researchers aren’t sure how the Ectobius genus made its way from North America to the Eurasian continent. One theory suggests the cockroaches traveled through Beringia, the area between Alaska and Siberia, then made their way into Asia and Europe, traveling east to west. Another theory posits the cockroaches crawled from Canada to Greenland to Scandinavia and beyond. Researchers believe this would have been possible during the Eocene Epoch as sea levels were much lower and continents closer together. Once in Europe and Africa the species thrived, though became extinct in North America not long after.

A cockroach on a leaf
Modern Cockroach (Ectobius) | Adam Opiola
Researcher Conrad Labandeira from the Smithsonian National Museum of Natural History said this of the Green River cockroach fossil discovery: “Much of our science is actually unpredictable in the sense that you never know what you are going to find. You open the door and there are mysteries. So this is an example of finding something out of time and out of place, and it leads into a very different interpretation of what actually happened.”

Root Weevil (Fremont Archaeological Site)

Folsom-era weevil abdomens from Fremont Site near Gunnison, Colorado
Root Weevil abdomens from Fremont archaeological site | Bob Hammon, Colorado State University

Tenderfoot Mountain, a vast mesa located in the Gunnison Basin, was home to an ancient civilization called the Folsom people 10,000 years ago. These early inhabitants hunted bison by chasing them across Tenderfoot Mountain’s flattened top until the charging herd arrived at the ridge line, where the bison closest to the edge fell off to the valley floor below.

As researchers identified and excavated the site of the Folsom community atop Tenderfoot Mountain, later named the Fremont archaeological site, other discoveries came too. Some were manmade implements, like Folsom-point arrowheads, crude sewing needles, stone tools for processing hides, and debris sloughed off in the tool-making process. Others were evidence that an undescribed species of root weevil, never seen before, had lived alongside the Folsom people.

Hundreds of these well-preserved root weevil abdomens were found in the rocks 18 inches below the soil surface. Examining the abdomens, researchers determined these 10,000-year-old Folsom era root weevils belonged to the undescribed Dyslobus (near) wasatachensis species.

In the modern day, root weevils are a pest that can devastate crops. They nearly destroyed the U.S. cotton industry in the early 20th century. One can’t help but wonder if they were a pest to the ancient Folsom people as well.