Can I just say, without any implications, that the Irish way of saying squirrel is adorable? One of my Irish friends said it yesterday and I had to fight not to tell him it was adorable because he was being very serious about this nasty invasive pest. Squee-rell.
People hate the grey squirrels because they are driving down populations of the native red (adorable) squirrel. The main problem with the grey squirrels is that they carry a pox that the native squirrels have no resistance to (see American chestnuts), but they also compete for resources and habitat. They also strip bark from trees.
Also, similar to the European Starling in the US, a small population was introduced at the beginning of the 1900’s and they have since colonized the entire country.
I have to say, even in the US where they are native, we prefer our red squirrels. But I still like these nasty, invasive, aerial acrobats (tree rats as my dad would call them).