Hard to say without knowing where they'ce come from. If, for example, they are lime aphids then presumably they're come in from outside (are there lime trees nearby?). If it's another species then it's anyone's guess as to where they're from. Do you have any indoor plants?
Ni Lime trees around or any indoor plants. It's a real mysery, have a large oak tree and there has been some suggestion they are either gall wasps or chalcids but no real concrete i.d. As I say have hundreds ?thousands in property but not sure where they come from. Sorry everyone, I suck them up thew hoover at the moment which I really hate, they seem to have qquite a hard shell. Don't like to kill them but would rather they are outside!!
I'm pretty sure they're aphids. If you could get a good picture of a healthy specimen it might be possible to give an ID but there's no guarantee. Have you any vegetation growing up the side of the house?
Sorry my computer crashed, have added some more pictures, but not vry clear i'm afraid as my camera is unable to zoom in enough. In reply I have no vegatation around the property, this has been going on since May 2012!!