Posted: 14/05/2014 at 06:16
I suspect that they're aphids of one sort or another. They suck the sap and weaken the plant and they keep breeding so there are more and more.
You can mix up a weak solution of washing up liquid and water and spray them - you'll probably have to do it a few times but it usually gets rid of them.
If there's a lot you can brush the worst of them off before you spray - either with your fingers or if you're squeamish with a soft brush, then spray the ones that are left.