All of my Twitter contacts are in my phone contacts, how do I remove them!?

I have gone into my contacts on my iPhone 6 for the first time in ages only to find that everyone I follow on Twitter is now in my phone contacts. I feel like this is a super annoying and unnecessary feature as I don't need random celebrities in my phone book as its not like I can just call them!?

I have no idea how this happened, can anyone tell me how I can remove them as I now have hundreds of unwanted contacts on my phone