I have seen so many of these little critters, looking mostly like balls of fluff or a bit of debris, until they start moving. I had no idea what they were but today managed a non-blurry shot and thanks to the good folk at Bug Guide, I now know it is a lacewing larva underneath all that stuff. On top of the pile there was a tiny exoskeleton of a spider! Bug Guide also notes that they may have evolved to do this as some protection against predatory lady beetles. Interestingly, the green lacewing larvae are themselves predatory on aphids, sawflies and other insects.