The Arquillians (also spelled Arquilians) are a race of tiny humanoid aliens. Arquillians have large heads and eyes, but have a small body, resembling tiny versions of the so called "greys". Due to their small size, Arquillians hide in human-like exosuits. The Arquillians are the possessors of the Arquillian Galaxy and will not stand for it being lost or stolen. The Arquillians also have a royal family, implying that they have a monarchy.
In the original film, Edgar the Bug comes to Earth to steal the Arquillian Galaxy. During his quest he finds and kills two Arquillians. At the morgue, Jay discovers that Gentle Rosenberg, a member of the Royal Family, is not yet dead: before dying he tells Jay and Laurel, the morgue attendant, that the Galaxy is on Orion's Belt. Jay relays this information to Kay and Zed, who are confused as Orion's Belt is three stars, not the billions needed for a Galaxy. After talking with Frank the Pug Jay realizes that even though the Galaxy comprises billions of stars, it does not have to be massive on a human scale. He then realizes (as does Laurel and the Bug) that the Galaxy was the sphere on the collar of Gentle's cat, Orion. At this time, the Arquillians threaten to destroy the Earth if they cannot retrieve the Galaxy. Jay and Kay are able to retrieve it, saving the Earth.
In the animated series episode The Long Goodbye Syndrome, Jay and Kay are sent to help an Arquillian who is choking on seafood. They help him, and he comes to thank them. However, when he hears about Jay's predicament, he tells Jay he might as well have jumped off the Empire State Building.
They are also shown to have an enemy in the equally minuscule species called the Fmoo.