In the northwestern United States, this crayfish would be just a friendly bit of local fauna. But in Scotland, it's an invasive species wreaking havoc on trout streams. Ari Shapiro/NPR hide caption

itoggle caption Ari Shapiro/NPR

A commercially harvested crayfish from Lake Tahoe near Incline Village, Nev., in July. Max Whittaker/Prime for NPR hide caption

itoggle caption Max Whittaker/Prime for NPR

The new species, Barbicambarus simmonsi (left) is more than twice the size of typical crayfish found in the same creek. L. Brian Stauffer/UI News Bureau hide caption

itoggle caption L. Brian Stauffer/UI News Bureau