Megaworms

These giant beasts are residents to certain Bacterian worlds.

Apparently a large Megaworm had been sleeping deep under the surface of Bacterius and was awakened due to some seismic activity. The ensuing situation saw the huge worm wake up and wreak havoc to a nearby city. This took place some time after the creation of the Inter-Stellar Alliance.

The ISA forces had to use atmospheric fighters and other military forces to kill it. The creature had immensely tough "skin", for the lack of a better term.

It is assumed the worm was indigenous to the planet, and not in fact a bio-engineered weapon - but with the Bacterians, who can tell.