There are parts of the world where squirrels are invasive species. For example Grey Squirrels are invasive to the UK if I recall?

Edit, I just looked it up to fact check myself and yeah Eastern Grey Squirrels are invasive to the UK and parts of Europe and are a threat to native red Squirrels and the like. Ironically, they were introduced to the areas they're now invasive in because people liked their aesthetics and wanted to hunt them. People are absolute idiots.