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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 , is currently leading the collaborative project with U.S. and Canadian researchers. A survey of nearly 2,000 teachers found that schools had released dozens of well-known invasive species, like crayfish, waterweeds, mosquito fish, and red-eared slider turtles (above).

In addition to reaching out to educators, Chan and his colleagues have also encouraged several leading biological supply companies to send region-specific specimens. But this poses challenges because each captive species has specific food and habitat requirements, which may be unknown. And higher mortality rates are a headache for cash-strapped school districts.

Meanwhile teachers—and their students—are also finding alternatives to release or euthanasia. Classrooms with crayfish, for example, study how the animals are a large part of southern culture and end lessons by hosting a traditional Cajun boil. “One of the best parts of this project has been seeing how creatively teachers are solving the problem,” says Chan. “And also seeing how children are enjoying a more comprehensive look at the animals they are studying.”