Serfian

Serfians were insect creatures derived from a simple drug integrated through an injection.

Biography
The Doctor and Donna discovered that Humans were transforming into these creatures because of an injection supposedly used to help ease an injury.

Sergeant Lenova turned out to be a Queen of the species, and had been producing millions of Serfians for a long time and storing them beneath the medical camp. These Serfians multiplied and were prepared to start an invasion of the planet Rescension instead of allowing either the Aquabi or Human to succeed.

They were hunted for a long time by giant robots, who slaughtered the Serfians because of their forced evolution into the universe. The Doctor and Commander Perdova used one of these robots to end the Serfian's invasion. (NSA:  Pest Control)