Chris Smith is on a hunt for buried treasure.

A short hike off a road in the Sherburne National Wildlife Refuge, near Zimmerman, he drops to his knees next to a hole in the ground that’s been covered with chicken wire, plywood, and a concrete weight. As he removes the makeshift cover, a sickeningly sweet stench wafts out. Smith, a Nongame Wildlife Biologist with the Minnesota Department of Natural Resources, wrinkles his nose as he reaches into a buried five-gallon plastic bucket and pulls out the deflated carcasses of two very dead, very rotten rats.

Secured from a local reptile food vendor and aged several days in the back of his work truck, the pungent rodents are bait for the objects of Smith’s search: the American Burying Beetle (Nicrophorus americanus), a federally listed endangered species that used to be found across the eastern half of the country. Now it’s known to survive in only a handful of states. Black and orange and sometimes nearly 2 inches long, it hasn’t been seen in Minnesota since the late 1960s.

The ripe carrion Smith buried the day before in what’s known as a “pitfall trap” attracts a variety of burying beetles from anywhere within about a half-mile radius. He sifts through a shallow layer of sand at the bottom of the bucket, removing beetles one by one, calling off their scientific names so that his colleague, Erica Hoaglund, can enter the information into an electronic tablet.