A genetic mutation of the UK enemy squirrel threatens to out-grab even the wild and power-hungry greys:

This from 2008 – seems to have been affecting East Anglia mostly. Not sure what’s happening with them now.. been quite in the news.

The black squirrel – a genetic mutation of the grey – was first recorded in Britain 90 years ago but now accounts for half of all squirrels in some parts of the country.

They have higher testosterone levels, which is thought to make them more domineering and territorial, while their colouring makes them more attractive to female greys.