Silk worms at 9 days old.

At first glance they look like cinders. They have the same greyness against the barely-green feed. Before they move they look a little like the remains of twigs, or maybe the fossilised remnants of coral or brachiopods. It takes a short time for my eyes to adjust. It is like looking into the dark. Then, perhaps in response to the lid coming off and a short rush of cool clean air, they stir a little. Some are like cobras; they lift the swelled and slightly flattened head-ends of their thoraxes, and sway before me. Only then does my eye truly fasten upon them and I can see them.

Silkworms with scale at 1 cm intervals

They are about a centimetre long now and their bodies have filled out a little more so they look like real caterpillars. It is becoming easier to distinguish them. There are different colours and different markings. Some are a pale brown, but the rest are varying shades of grey. Some don't move at all, and on closer inspection these immobile silk worms are clearly moulted skin. Perhaps they are the first moult. However it is difficult to see which have moulted and which have not because there is no dramatic change in appearance.

Silkworm with moulted skins

I read somewhere that they only make silk in their last instar, but maybe that should read they only make copious amounts of silk in their last instar. The silk glands are clearly there from the start because apart from the fine mat of silk that soon coats their food, they dangle from my tweezers like a spider when I try to clear out their box. But whereas such a captured spider would frantically spool out more silk and escape, the silkworm is more nonchalant. It doesn't struggle. In fact it barely moves. Instead it seems to wait patiently (or mindlessly) to be placed somewhere else. After all, a silkworm is close to being a manufactured animal. For years they have been bred in captivity and cannot exist in the wild. They exist because men have made them so. It is as though they passively accept their lot, ponder over us a short while with their raised heads, and then continue grazing.

Silk coating food

The Squirming Mass.

(Click on the image for full effect).

From a distance the food looks like some indeterminate lump of something green, but on closer inspection it is possible to see that the lump is, in fact, covered with a mass of constantly moving tiny brown hairy caterpillars. Underneath I can see that they are each eating away a small furrow and this is giving the mass a spongy texture.

As I move in closer it seems like the larvae are hovering in mid-air as if already they are spinning silk. Perhaps they are. They already move as their parents moved when searching for a place to spin: their hind quarters locked into position and their black heads, outlined by a paler thorax, circling the air, presumably sniffing for food. Perhaps they have chemical receptors that will react to only one thing: mulberry leaf.

Anyway, the whole effect is slightly revolting, so I just had to share it...

Added Later.

Looking at the photograph I can see now why the eggs grow darker. I'd thought it was just that the egg-case hardens and darkens as a consequence. But on closer study I think the darkening is due to the black caterpillar forming inside. The indentation in the surface is because it is curled around itself in a ring. The case of the egg, I think, remains translucent, and as the caterpillar grows it becomes more darkly pigmented.