The symbiots have appeared as a result of discovering of the Arling project by Super. This project was frozen down at the demand of the Creators back in the times when the range was still in making. Apparently the Creators were afraid of the possible outcomes of such studies. Super has none of their fears. And that was how the symbiots appeared.
Basically this is a sub-variety of mechanoids, but of organic, rather than molectron origin. They are being grown deep underground under special conditions. The same method is used for other organic structures such as glider bodies, sensors and many others.
The symbiots largely prefer to use organic gliders, which is most likely related to their own origin.