Silkworm pupae in bales of straw.
We have another photo showing silkworms at an earlier stage, while they are still busy feeding on mulberry leaves.
When the caterpillars decide to pupate they weave themselves white silken homes. A silkworm farmer provides straw as a convenient warm and dry location for the creatures to weave their precious silk wrappings.
The silk can then be harvested by separating the pupae from the straw and spinning them into thread.