Black aphids

[mothhawk]

I'm having a problem with black aphids. Not on my plants. Every morning for the past 6 or 7 days, my front door sill, which is white, has been covered with these aphids. There are none that I can see on the roses either side of the front door, and they don't have wings, so are not flying here. I'm at a loss to know where they are coming from, and why they are congregating on my doorstep. i've sluiced the step every day with soapy water to get rid of them, and the next morning there are more again.

This is the few that have come since I washed the step today

[Nicos]

Hmmm…how strange!
I don’t suppose you have a cherry tree nearby?

[mothhawk]

No cherry trees. There are acers and a linden tree up the road, that's all.

[nvidura]

Nearby, there may be a plant or another source they’re feeding on that’s just out of sight, such as the undersides of leaves or the stems of plants not directly in front of your house. Soapy water is a good approach, but adding a mild neem oil solution can further deter them. Also, inspecting nearby hidden areas might help locate any small colonies that could be the source.