Silkworm cycles

Yesterday, at dawn, my last silkworm emerged from her cocoon and promptly started to mate. This morning she has laid some eggs. I have a feeling this may be the last clutch. Other matings seemed to have yielded no eggs at all. I think maybe these held on to each other too long because now they seem to be almost dead with exhaustion.



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.


And 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.

Silkworm Reproduction

I lift the lid. I know the sound by now; a desperate throbbing of wings. Two silk moths huddles together - the tip of his abdomen inserted into the tip of another. I feel like I shouldn't be watching, but I do. In fact, I am mesmerised.



Clearly it requires effort. Slowly, it seems, this male moth is pumping all that remains of his life into hers. All those days of eating, eating, eating - all for this. It goes on and on, day after night after day. A short rest and then he starts again: a fast beating of the wings, the tiniest shove. And she just sits there. Fatly immobile. Docilely smug. As soon as she emerges they are after her. A little eau de Bombxyol behind a middle segment and she could be anyone's.

Then, a day or so later, they will mysteriously detach. He might busy himself with a search for another, but shortly thereafter he will die. She, meanwhile, will excrete one glistening yellow drop of liquid - the remains of whatever toxins remain inside her - and then will start to lay her eggs. She places them delicately, her abdomen tip describing circles and lines, one egg and then another, beads the size of pin heads, a production line of seeds to harden, darken and eventually become another - just like her.

A Menage a Trois

Well there are only five occupied cocoons now - and so far my cocoons have yielded five females and twelve males; five of these males are of course very happy... and the rest very frustrated. So frustrated, in fact, that this morning I discovered that one newly-emerged female was somehow mating with two males at the same time (I did not take photos). I prized off the more disreputable-looking one and put the remaining pair in the 'ovarium'.

Here is a short clip I took a couple of days ago of a recently-emerged female attempting to dry off, and the males just starting to pay her some attention.




I wonder if it is usual to have such an imbalance of males and females. I know in other insect colonies this is the case, and I can see why - but I don't really see why there should be in a population of silk moths.

An Unhealthy Obsession.

Great excitement among my male silk moths this morning; each one was wildly flapping his wings. The reason was that another female moth had emerged. Already one male had mated with her, and another was trying to attach himself to her too. Now that I know about the pheromone, it all makes sense.

I removed the extra male as gently as possible, and then put the mating pair (stripy male and female) in another box to give them a little peace. At once the rest calmed down. That pheromone is a powerful molecule, but it seems that once the source is removed the effect soon fades away.

I then managed, at last, to separate yesterday's happily mating couple (stripy female-unstripy male), removed the male, and after waiting a few seconds replaced the paper under the female - which was now dirty. She then promptly started to lay her eggs. It were as if I had given her permission.

I am trying to leave the silk moths alone now, and divert my mind back to the Patagonia novel. I want to try and finish the Tehuelche edits this week because I have to give in the revised manuscript to my editor at Seren in March.

The Clinch.

In fact there was no need to do my light experiment, because when I woke this morning I discovered that two more moths had emerged overnight and one of them - which was huge with eggs - was in the process of being fertilised by one of waiting males....So maybe they were all males after all.

I have tried to separate them just now because I thought they had been mating long enough (they are only 'supposed' to mate for three hours) but I was unable to break their clinch. I have transferred them to my 'ovarium' (a box with a wet flannel over the top inside another box with a lid in an attempt to keep them humid enough).


I have also put them on some glossy paper in case this proves to be a better medium for eggs than newspaper.