The documents filed Tuesday say 37-year-old Sven Koppler of Wachtberg, Germany, signed a plea agreement over the weekend involving one count of smuggling goods into the U.S.
He could face up to 20 years in federal prison when he is sentenced April 11.
Federal prosecutors say Koppler mailed more than 240 live tarantulas from Germany to Los Angeles last year. Fish and Wildlife Service agents intercepted the packages then posed as customers and ordered dozens more spiders, including a protected Mexican species.
Authorities say Koppler made $300,000 by selling spiders to people in dozens of countries.