In the 1970s an Alaskan high school science teacher purchased red-legged frogs from a supply house in the Pacific Northwest. Once the amphibians were no longer needed, the educator released them. Four decades later, studies show that frogs that have decimated local Alaskan populations have genetic ties to those found in Washington’s Columbia Basin.Specimens bought in pet stores or shipped from biological supply companies typically aren’t native to the places they’re studied. When the lesson or school year is done, teachers unwilling to euthanize classroom animals often set them free in the wild, where they can overrun an ecosystem while displacing local species. A new program is working to educate teachers about the dangers of letting aliens loose.Sam Chan, a biologist who researches invasive species at Oregon State University, is currently leading the collaborative project with U.S. and Canadian researchers. A survey of nearly 2,000 teachers found that schools had released...