Another set is Yandex, a Chinese [Edit: Nope, Russian, see below] web crawler. I've done a basic "what CIDRs and ASNs were involved" in a top-level post.

These idiots can't tell Web crawler traffic from DDoS (though often there's little practical difference).

Probably an amplification attack using Google, a clever way to increase the size of an attack without adding too much additional cost.