life and death and mail-order caterpillars

A month ago, we sent away for caterpillars.
Three weeks ago, they arrived in the mail.
We watched them eat.
We watched them produce five times their weight in caterpillar dung.
We woke up one morning to five chrysalises.
We waited.
The butterflies emerged a few days later.
They dried their wings.
They fluttered around a bit in their net but did not fly.
They pressed their bodies together, mating in captivity.
Yesterday, we let them go.
They flew, awkwardly at first.
They stayed close, swooped around our flowers and circled back for several minutes.
Then they were gone and we took the empty net back inside.
Today, in two milk lids taped together, we buried the one who died midway to maturity.
My son is sad and I tell him that it's part of nature. We can't help it if sometimes nature is cruel, sometimes butterflies just don't make it. He seems to accept this explanation.
But I can't get over the image of the tiny interrupted thing, its sticky wings caught in the cracks of a chrysalis shell so thin it is already turning to dust.