Our native Red Squirrel, which is very cute (see pic), has all but been replaced by the alien Grey Squirrel, which is not. But, if you have never seen a Red Squirrel, the Grey is better than nothing.
The problem is that the Grey is bigger and more aggressive than the Red, and outcompetes it for food. There have been attempts to reintroduce the Red Squirrel into woodland using an ingenious feeder, which has a hinged platform in front of the feeding hopper that will take the weight of the Red but not the Grey.
Unfortunately, there is strong evidence that the Grey carries a lethal virus to which it is immune, but which is a killer for the more delicate Red.
It's a bugger, isn't it, when Might is Right?