The silk is produced from spinnerets, two apertures in the head, the two
filaments joining as they appear to form a very strong thread from five
hundred to one thousand yards long. This the caterpillar wraps round its
body until it is completely covered, and then it passes into the
chrysalis state. Unless the grey moth is wanted for egg-laying, the
chrysalis is killed by putting the cocoon in a hot oven, for if allowed
to appear it cuts through some of the more valuable parts of the silk.