Aerovores (Gray Dust)
A form of goo replicator constructed almost solely of CHON (Carbon, Hydrogen, Oxygen, and Nitrogen), and hence able to replicate relatively rapidly in a standard Terragen-like environment using only atmospheric resources and powered by sunlight.
The use of aerovores is banned by all conventions of galactic warfare, but they have still been used on a number of occasions throughout history, including during the Conver Wars and the Sagittarius Frontier Wars, and, more recently by the Xeon against stubborn targets.
The most efficient countermeasure strategy involves the use of air-dropped blue goo (including semi-replicators and non-replicators) nanorobots equipped with prehensile microdragnets. In addition, airborne and ground-based atmospheric filtration configurations enable removal of individual units from the air.
Since drag power varies as the square of the velocity, increasing mesh volume 10,000-fold while decreasing airflow velocity 100-fold, means that total drag power remains unchanged but whole-atmosphere turnover proceeds 100-fold faster.