When Beatrix Potter wrote The Tale of Squirrel Nutkin, it was 1903, and the squirrels that populated her books were the English countryside’s native Eurasian red (Sciurus vulgaris), with tufted ears, russet red fur, and a flair for the dramatic. About thirty years previously, their American cousin, the eastern gray squirrel (Sciurus carolinensis), had begun making the transatlantic crossing, brought by the English seeking to add the newly fashionable creatures to their gardens, landscapes, and homes.

One hundred and fifty years after their introduction, the gray squirrels outnumber reds 20 to 1 in the United Kingdom, and scientists are proposing to genetically sterilize them. What happened?

Squirrelpox is one answer, specifically squirrel parapox virus. Gray squirrels carry it and red squirrels have no immunity to it, which has led to a significant decrease in and consolidation of their population. Compounding this is that gray squirrels can eat and digest green (not fully developed) acorns, leaving red squirrels with a smaller supply of digestible, mature acorns.

Enter the Roslin Institute—the Scottish research center that brought the world Dolly the Sheep. Researchers there have proposed using a gene drive to help control the population of the invasive gray species, ultimately resulting in their disappearance from the UK and the resurgence of native Tufty Fluffytails everywhere.

A gene drive is both a method and a construct. Using CRISPR, the desired gene (which can be new, mutant, or modified) can be integrated into an organism and released into the wild. Then, because of the structure of the drive, the gene will be inherited more frequently than normal (approximately 50 percent of the time) and thus “drive” the gene via sexual reproduction.

In the journal Jurimetrics, the authors examine the use of gene drives through a legal lens, asking questions about what responsibilities we have to future generations when using these technologies, and how unintended consequences of their use might impact them (for example, if invasive species’ gene-drive carriers were to come in contact with native populations of the same species). Different approaches to invasive species, and the issues with each, are outlined: immunization to the invasive species, sterilization, enhancement of predators of invasive species, and sensitization of native species to some relatively safe agent that might then be used as a control mechanism.

The use of genetic engineering to remove the eastern gray squirrel from the UK may be complex, expensive, and possibly result in a squirrel dystopia; however, earlier suggestions were a bit more bleak: kill, eat, and/or wear them.

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