A possibility here? I found this abstract from an article in Science magazine (you have to subscribe for the full article, so can't see if there are any pictures)
"Wolf-in-Sheep's-Clothing" Strategy of a Predaceous Insect Larva -- EISNER et al. 199 (4330): 790 -- Science
The larva of the green lacewing Chrysopa slossonae lives in colonies of the wooly alder aphid Prociphilus tesselatus upon which it feeds. It disguises itself as its prey by plucking some of the waxy "wool" from the bodies of the aphids and applying this material to its own back.
I can't say I saw any aphids on the tree it was on - must go back for another look.