When you are trying to decide whether to hyphenate something, try this:

...It is a large green bug that....

It is a bug. What kind of bug? It is a green bug. What kind of green bug? It is a green bug that is large. If this works and you can "build" it like this, it is not hyphenated.

...It was a small black car that....

It is a car. What color car? It is a black car. What kind of black car? It is a black car that is small. When this works, it is not hyphenated.

Happy punctuating!