self assembling particles
 

scientists have made nickel particles able to assemble themself to bigger units by using surrounding material.
Dont anyone see science fiction at all, this is how the "asgards" in stargate 1 were wiped out. This is how aliens wipe out life on planets deemed to violent in "the day the earth stood still" just to name a couple.
Watch the following:
YouTube - Self-assembling magnetic "snakes"

Hajeeze...