Can anyone identify this insect for me? There were thousands crawling up the trunk of a conifer and all over its branches at a Buckinghamshire pre-school last week. The children and staff are very curious about them and their sudden appearance. Any help would be much appreciated.
They're aphids, a Cinara species I think. They're feed on the tree but I don't know why they go into this dispersal mode and walk down the trunk - maybe because it's getting a bit congested with them on the tree.