The pupae are enclosed in dark cocoons. To prevent this, silkworm cocoons are boiled. The silkworms that hatch weave cocoons containing 10% spider protein. RSF is produced by chemically dissolving silkworm cocoons, leaving their molecular structure intact. Mature larvae that make silk also make threaded cocoons. The wasp larvae feed internally and emerge from the body to spin their cocoons. Lefty makes a living selling silkworm cocoons harvested by his sister, Desdemona. Another version says that she found silkworms eating the mulberry leaves and spinning cocoons. Chinese sources claim the existence of a machine to unwind silkworm cocoons in 1090. The heat kills the silkworms and the water makes the cocoons easier to unravel. Another metaphor is that caterpillars have to climb out of their cocoons to escape. Once the wasps have emerged from their cocoons, the weakened caterpillar dies. Pupae may further be enclosed in other structures such as cocoons, nests, or shells. The larval Mothra swims to Tokyo and cocoons herself around the Tokyo Tower. The soft, silken cocoons make an interesting keepsake for pupils.