Squidheads appeared mid R. 2,009 along with various other alien species, some evolved from older forms of life, some from the backasswards planet in the middle of nowhere.
Squidheads fill the underworld fringe cities, working for anyone willing to print up some flats with 100 on them. Generally if a squidhead lacks one of these specific 'Bills' they tend to do whatever they can to receive or retrieve another, going even as far as serving in sweatshops, raiding their parents money jar (which is sure to be full of these), or stealing, though they may insist that they were just 'borrowing' said 'bill'.
Nonetheless they will often be killed on sight in most empires if they are not being used for some labor, or are imprisoned by the now resurgent space police. Where they are imprisoned is not currently known but it is believed in keeping with their more 'civil' ways the space police deposit them on quite habitable swamp worlds, with plenty of basic colonization gear. But it is believed that by using some unheard of knowledge they produce modified engine parts then open these planets for trade with the wider galaxy if they are not wiped out first. They have the spider gymnastics ability due to suction cup feet.
Rumors of another of purple type of squidhead, called squid-trons(short for squid-darktron) are thought to be cooler than they're green counterparts.