I built a base where I circled, it is on one of the lower stone slabs around the pond. Part of the idea was to build a tower up to the upper garden there for easy of access.
However after doing this, somehow despite never seeing it spawn down here before setting up a base, an upper yard Ladybird (Yes the aggresive ones normally only in Upper yard) has spawned inside my base.
So it seems not only can bugs spawn inside bases if their spawn point is normally there, but things with a big area they can presumably spawn in can start registering bases as a spawn location.
Here is a picture of it in my base:
