Who's hijacking my dahlias?

Doing the rounds this evening I notied several of my dahlias have hundreds of little hijackers. They're not on any other plant but several of the dahlias have them clustered around the main stem, mostly just below the buds. No obvious damage as yet. Thoughts on (a) what they are and (b) how to get rid of them (assuming I need to)?

 

They just look like aphids to me - soapy washing up water and a little squishing should clean them up.

 

I have them on my climbing roses. I do what Tetters says it does get rid of them, just be carful of how much soap you use, my first attempt burnt the roses fresh growth, I now use 7/8 drops of fairy washing up liquid for a full spray bottle,

They did come back after a while, I sprayed them with the above mixture aphids disappeared and new growth appears fine.

 

Agree with @Tetters , I do he same and it does the job well