These are all that are left. The majority have died. They seem to die gently and gradually, life slowly leaving them, and I pick them out and place them alongside the cocoon. How shrivelled and small they seem to be now. All that huge consumption of mulberry leaf extract has led to is this.
Where does it go? I think the answer must be into the air: starches converted to sugars in the gut of the silkworm and then stored as fat, must eventually be consumed in the business of mating to produce energy and carbon dioxide and water...which the mulberry bush could one day use again to produce more leaf. It is a pretty cycle.
In some parts of china the silkworm-mulberry plantation, together with a fish pond, provide a self-contained ecosystem for a small community. The silkworm feeds on the mulberry and produces cocoons. Its waste is fed to the fish; white the pupa provide useful nourishment to the growers. The sludge from the fishpond is used to fertilise the mulberry plants, and the fish themselves are another source of food. I like the way nothing is allowed to go to waste. An extension of this idea - the use of silkworms as a useful food for astronauts - is reported in March's edition of Scientific American. Pupa not only contain fat, but four times as much protein as eggs and milk. Also 'These insects breed quickly, require little space, food or water, and produce only minute amounts of excrement, which could serve as fertilizer for onboard plants.'
I am not so sure about 'little food' - but I suppose in comparison with most mammals and birds silk worms are indeed very efficient converters of plant into animal.