Mutant spider (Arachnids in the UK), since that's the term preferred by Case File Four.
Talk about it here.
The spiders were led by their mother, which was larger than the others. As it was suffocating by its own size, Robertson shot it, murdering it. The spiders were eventually contained through the efforts of the Thirteenth Doctor, Ryan Sinclair, Graham O'Brien and Yaz. (TV: Arachnids in the UK)