Most mornings when Eric Larson hauls a wire-mesh trap into his fishing boat on northern Wisconsin’s Trout Lake, he finds dozens of coffee-colored crayfish wielding their oversized pinchers in a frenzy, trying to fight their way out.

Larson, an ecologist at the University of Illinois Urbana-Champaign, records each animal’s shell length and sex. Then he places them into a bucket of water laced with fish toxicant, an ethically approved form of euthanasia for this invasive species. At Wisconsin’s Trout Lake, and other lakes nearby, Larson and his team can catch, study, and euthanize a couple thousand crayfish in just a few hours. 

Native to the Ohio River and named for the rust-colored splotches adorning their shell, rusty crayfish