Wooly Oak Aphids

I received a call from a client who complained that their oak tree was dropping fuzzy stuff all over the area underneath its canopy. I asked them to bring it in and this is what I saw:

Leaf with cottony wax and visible aphids. 

I then put it under a magnifying scope and was able to see the culprit:

Closeup showing (l) aphid, (r) egg surrounded by waxy 'wool' produced by the aphids.

It was Wooly Oak Aphid, one of a pantheon of insect pests that attacks oaks. Like many pests on oak it is mostly not a threat, just a nuisance. Time is the usual insecticide, with infestations resolving themselves within a month or two when increasing attacks by predators and the changing physiology of the oak itself lead to its demise.

Links to more information on the Woolly Oak Aphid:

Woolly Oak Aphids - BugGuide.Net

woolly oak aphids, Stegophylla brevirostris, on black oak leaf. - YouTube

Aphids Management Guidelines--UC IPM

woolly oak aphids -Stegophylla brevirostris Quednau and Diphyllaphis microtrema Quednau

Dancing woolly aphids will probably stab you - Scientific American Blog Network