I found them on one vine of the Ivy plant that I bought from Ikea about a month ago. It was kept about 2m away from my other plants, so I'm hoping that the little guys haven't had the chance to hop over.
I've also liberally cut off the visibly affected branch and sprayed off the Ivy in the shower, followed by a generous misting with soapy water. The plant will stay quarantined in my kitchen for the next few weeks, hope it recovers :<
My other plants seem fine so far, at least I couldn't find any critters on their leaves when I checked tonight.
Honestly you're better off dumping the ivy. They're not fantastic houseplants as they are very prone to insect infestation and seem to attract spider mites, particularly in winter.