Dark spider found in Idaho could reveal a remnant mountain ecosystem scientists nearly missed

A University of Idaho team says an unexpected spider found in Idaho could matter for more than classification alone — in their view, it may also highlight a rare piece of mountain habitat that persists in only a very small forest area, Hagadone News Network reported.

Here's what to know

University of Idaho researchers indicated that the newly described arachnid seems limited to an isolated section of damp conifer forest in the Nez Perce-Clearwater National Forests. 

They believe surrounding dry conditions, higher terrain, mountain features and, in some places, rivers may all help keep the population cut off.

The researchers have identified the previously unknown spider species and named it Hexura vandal after the school's mascot. 

The dark, nickel-sized spider was formally described in an Aug. 31 paper by doctoral student Arnau Calatayud-Mascarell, former postdoctoral researcher Ethan J. Briggs, and associate professor Chris Hamilton.

It was published in the journal ZooKeys.

The spider was found Sept. 8, 2024, near Kooskia, while Calatayud-Mascarell and Briggs surveyed the Lochsa River for dissertation research on the genus Microhexura. 

During that work, Briggs spotted a spider that appeared to belong to Hexura, a genus previously recorded in Oregon, Washington and British Columbia, but not Idaho.

"We didn't care about Microhexura at all after that. We found something way, way cooler," Calatayud-Mascarell recalled.

Hamilton believes the find challenges the assumption that the country's species have already been mostly documented.

"I think people assume that the U.S. has been pretty well picked over and we have an idea of all of the species in the U.S., and that's not true at all," he stated. "This is a great example of that."

More background

Researchers noted that the Idaho spider looks different from the other two known Hexura species in the Pacific Northwest. 

Unlike many closely related mygalomorph spiders, which often need genetic testing to be separated, these Idaho specimens were visually distinct, and genetic evidence backed that up.

The team suspects the discovery points to a long period of isolation. On repeated visits to the area, they found many of the spiders within a core habitat of moist conifer forest, mossy ground, and decaying logs.

In the drier surrounding landscape, however, the spiders were no longer present.

Researchers said that abrupt transition could be a biological sign that a small vestigial ecosystem is still persisting in the mountains of north-central Idaho.

What's being done?

After confirming the first specimens, the researchers made several more trips to define the spider's range and learn more about the habitat conditions it depends on.

That work could be especially important if the species truly occupies only a very limited area, as the team surmises. A spider restricted to a single damp forest pocket could be especially sensitive to drying habitat and other broader landscape shifts.

Hamilton suggested that the discovery could also have symbolic significance for Idaho. The state has no official state spider, and he suggested an Idaho-endemic species named for the state's land-grant university could be a strong choice.

"I feel incredibly confident that this is only going to be found in Idaho, and it's going to be restricted by mountains, increasing elevation and the drying out of habitats, and in some places the physical barriers of rivers, as well," Hamilton commented. 

"This species is an indicator of a unique, remnant habitat that's found in Idaho and needs to be looked at more closely and monitored."

Where can I learn more?

These stories look at other unusual spider finds and what they say about the places where they turn up. They range from newly identified species and rare wild discoveries to invasive spiders showing up in new areas.

• In Oregon, residents helped choose a name for a spider newly described by scientists.

• In the United Kingdom, conservation work led to a rare mini-tarantula discovery in the wild.

• In Pennsylvania, officials warned residents to watch for giant invasive spiders after a border-crossing sighting.

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