I've let this rest for a while, since none of the ideas went quite with what I wanted (though they were both good - AG's vanquished foes in particular sounds worth doing).
But I want still something different.
notes for later on, sketch of the enemies forming:
- predatory nature, as opposed to herbivores
- technologically somewhat below the Krylastys
- ?they are actually preying on the high-quality materials the Krys build their structures from
- special: ?claw-like weaponry - separating material on the molecular level - either some sort of beam or (sigh) monofilament wire - would require some exposure to the weapon to work
- coordinated attacks, synchronized targeting
- they cut apart the finest pieces of equipment and drag it away
- the Krys can usually defend themselves; but not their outer structures
- a typical attack means few casualties, but large damage
- most attacks are in freshly colonized systems; a few established colonies were attacked as well