When the Ur-Quan conquered earth, they did not believe that the humans would obey. Although not very powerful in means of ships, Humans were allways rebelious and cunning. Thus, the earthguard was born.
The earthguard was a group of hierarchy battle thralls, stationing near earth. At the beggining it consisted of Ilwrath and Spathi fleets. However, the Ilwrath soon departed, after hearing that ther twin gods, Dogar&Kazon are calling them. This is probably the point when they began attacking the Pkunk.
The paranoid Spathi were left alone however, when the last Ilwrath ship said that they will return "real soon", which actually meant never. Since they were aware of the fact that humans are rather smart creatures, they reocated from the base on the moon, hopping all around Sol, ending up finally on Pluto.
Thye left a base however to trick the Humans into thinking that the base is still occupied by Spathi and Ilwrath. They programmed it into looping "Winky's Happy Night" all the time in ardio frequencies, and programmed bulldozers to endlessly bulldoze the same piles of dirt, over and over. Since the Orbital station on Earth did not have the equippement to recieve the signal, only a part of it, they did not have a chance to notice the trick, and really belived that the base was occupied.
Destroying the base was the first task for Capitan Zelnick, given to him by the station capitan. When he arrived, one of the landers entered the base and gave him a report, in which the xenotech was sure that the signal is some sort of warning. After robbing the base, he departed to the starbase.