Let's go back to this plot, so what is the plot of the old man letting the insects feed the birds? From the picture of the old man asking for a bug to Andy handing it to the old man, we can see that Rhett and others are quietly observing Andy's movements. From their eyes, we can see that they are strangers to Andy, because Andy is sitting at the next table at this time, which has nothing to do with Rhett and his gang.
The old man's behavior of feeding bugs immediately narrowed the distance between Andy and Rhett, because the old man in our library and Rhett and others are deskmates, they must be familiar with each other, maybe they are friends, so let's infer first.
Andy gave the dead worm to the old man in a friendly way, and the old man's bird had a good meal, which was equivalent to helping the old man and establishing a good relationship of mutual trust and mutual assistance with him. Friends of friends are friends. According to this inference that nature conforms to normal interpersonal relationship, Rhett and his gang also have some favorable feelings for our Andy, at least on the surface.
Yesterday, when the cellmate who won a cigarette bet came over, he twisted his ass and sat in the only empty seat next to the old man. The whole table is full. Obviously, this is Rhett's inner circle.
It is through this little bug plot that the screenwriter brought Andy and Rhett closer. Many people think that it just shows that the old man cares about animals and loves life, or that he is lonely and only accompanied by birds. Of course this is one aspect, but think about it. Dead bugs will appear on Rhett's plate. Why are they on Andy's plate? This is definitely not a coincidence, it is intentional and carefully designed.