Shape stability would be an example of being less complex than insects.
And as you can see, we did not in fact know that in the 18th century. Transformations are not so easy to observe directly; they often happen e.g. underground.
"Shape stability would be an example of being less complex than insects."
Not if the shape is stable, because the underlying cells are too complex to merge into something different. Cells were known already. And that insects transform is known, but birds were closely known and there was not observation of them changing drastically. So that Aristoteles had this thinking is understandable given the time, but after enlightenment, I would not expect that from the early scientists.
