Silk Colouration

Hello Bill, My H. euryalus have started to spin. One thing that people often ask me about cocoons made from silk is "How come the wild silk moth cocoons are dark colored and not white like other cultured silk I have seen?" Well, I try to explain to them that they are white until the larva soaks them with a fluid that makes them both darker in color and hardens the silk making it into a protective weather resisitant structure. This is sometimes difficult to explain so I decided to take some "before and after" pictures to use in demonstrations.

The photo above depicts a freshly spun Hyalophora euryalus cocoon with another, spun earlier. The lower cocoon has not yet been impregnated with fluid while the upper one has. As you can see, the cocoon was pure white silk before fluid emission. The photo to the left also depicts how well these large cocoons (three of them) can be hidden in a small clump of leaves when the cocoons are darker in color, sticking out like a sore thumb when still white. I (Bill Oehlke) encourage people to watch the spinning and impregnation process. I am particularly fascinated by the striations in H. columbia cocoons. It will be interesting to learn if the surroundings at spinup time have any influence on the caterpillars' impregnation "strategies".

I have seen green cecropia cocoons as well as one of white silk, spun in a clear plastic tub. Perhaps the larva was without impregnation fluid for some reason.

by Scott Smith

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