Scrub Jubs are anxious creatures. they have hairs that cover their turgid bodies. These hairs are always in motion, sensing for danger. They apparently eat machinery.
They are a small species that inhabit at least one Covenant world. They tend to board space ships and eat the machinery. On a long space flight their numbers had to be contained in order to prevent them from damaging any vital systems. Therefor they are likely to be the equivalent of rats found on the Human home world Earth.
They are also used by Unggoy in a game where one has to kill as many creatures as possible, simply by using a rock. each kill is one point, no matter how easy or difficult the kill was.
Sources
Halo: Contact Harvest. page 89