Does “fives” still count if you wait 49 million years to come back? Photo: D.S. Shcherbakov

A group of allegedly “invasive” species of cockroach may in fact be able to lay claim to their current North American home as their own, thanks to the discovery of their 49-million-year-old ancestors in Colorado.

Since four species of cockroaches from the genus Ectobius were discovered in the US around 65 years ago, entomologists have believed the roaches were invasive species—the fossil record shows that Ectobius have been living in Europe for more than 44 million years. But it turns out the invertebrate has a much more interesting evolutionary and migratory history. 

Researchers have recently found fossilized ancestors of the species—all belonging to the Ectobius genus—near the Green River Formation in Rifle, Colorado. According to their study, published in the Annals of the Entomological Society of America, Ectobius likely originated in North America, migrated to Europe (back when North America was much hotter and the continents were positioned closer together), went extinct in North America, and eventually got reintroduced a few decades ago.

Does that make them an invasive species in the United States? Probably, as ecosystems have evolved for millions of years without the presence of Ectobius. It’s only been able to return to North America in recent years because, although it originally lived primarily in warm climates, it evolved in Europe to survive cold ones.

“One reason for the complete disappearance of this dominant genus from North America is the peculiar consequence that, after 49 million years, a cool-adapted Ectobius was capable of being reintroduced to a significantly cooler North America than its antecedents,” the study explained.

Though completely weird, the finding isn’t unprecedented. Horses were once native to North America but went extinct there 11,000 years ago in what is known as the Late Pleistocene Extinctions, where animals such as saber-toothed tigers, mammoths, mastodons, and giant beavers died off. Horses survived in Europe and elsewhere, and were eventually reintroduced by the Spanish.

Generally, Ectobius aren’t seen as pests and tend to live in forests and fields. That said, members of one species of Ectobius have reportedly become the “most frequently encountered cockroaches in urban areas of Switzerland,” even though they aren’t particularly suited to urban environments and can’t reproduce inside. And they’ve been known to invade at least one intensive care unit in Switzerland, where they were observed “hiding inside oxygen masks, moving around on the light panels below the ceilings, or dropping onto intubated patients during the night.”

The finding probably isn’t particularly important, but it’s one of those curiosities that tells us more about Earth millions of years ago and the crazy ways animals migrate and evolve to survive over time.