For sale is The Forge of God by science fiction author Greg Bear.
Book is a previously read Trade Paperback..

The Forge of God – 1987, Tor 2001. Trade Paperback. 1st printing.>
Earth faces destruction when an inscrutable and overwhelming alien form of life attacks. There is another alien faction at work, however, represented on Earth by small spider-like robots that recruit human agents through some form of mind control. In outer space, this faction's machines combat and eventually destroy the attackers but not before Earth's fate is sealed.