5 ideas
A dying butterfly leaves her eggs with a caterpillar, and a lark tells the caterpillar that the eggs will hatch into caterpillars and that it will one day become a butterfly itself. The caterpillar mocks both claims as absurd until the eggs hatch into small green caterpillars. That fulfilled prediction leads it to trust the promise about its own transformation, which then comes true.
Refusing to believe something only because it lies outside your own experience is a reasoning error, not caution, because your experience covers a tiny part of what exists. The sensible response to an extraordinary claim is to see whether the same source has already been proven right on things you can check. If it has, that earned trust carries over to the claims you cannot yet check.
Once a water-dwelling larva becomes a winged adult, it cannot return to tell those still below what the new state is like. This is because the two conditions cannot share a medium, not because the new state is empty. Silence from those who have passed into another state is therefore not evidence against that state.
The fables keep their natural history accurate and put the moral only in the characters' dialogue and the framing. Observation stays factually sound while interpretation sits on top of it. Because the facts are not bent to fit the lesson, the lesson borrows credibility from facts the reader could check.
Each creature judges what counts as superior using the abilities and senses it already has. As a result, it finds anything beyond its own scale either impossible or inferior. Seeing this bias in plants and insects is meant to make human readers suspect the same self-centred measuring in their own confident judgments about what is real.