Every year we try and obtain some silkworms, Bombyx mori, for the insects practical in Exploiters and Exploited, but we usually cannot find any for sale, as they are usually reared in the spring. This year we were luckier; I found a supplier with some in stock and they arrived on Wednesday, less than 90 minutes before the start of the first practical! Interestingly, these silkworms are not sold for silk production but to be reared as live food for pet reptiles.
The larvae arrived as first and early second instars (the instar is the stage in between moulting, in which the larvae feed and put on weight), only about 5mm long. They were supplied with ‘silkworm chow’ an artificial diet based on mulberry leaf powder. This is often used in rearing, and means that you can rear the silkworms when mulberry leaves are not available.
However, at Reading we do have mulberry trees, having established a small plantation of black and white mulberry a couple of years ago, and the bushes are now a reasonable size.
Thus, I have decided to try and rear some silkworms on their proper food, mulberry leaves. This is a tricky decision at this time of the year – mulberry is deciduous and it will not be long before the leaves senesce and fall from the tree (although they are pretty healthy at the moment), yet mulberry leaf is a much better food for rearing larvae to pupation, and thus for silk production. The problem comes if the mulberry leaves run out, as larvae then can be reluctant to go back to silkworm chow
So, on Wednesday afternoon I placed a couple of young mulberry leaves in the rearing container, and within minutes the larvae detected these leaves and started to move towards them.
The leaves were soon covered in larvae, and I removed them to a separate box and gave them more mulberry leaves. These are the first silkworms we have tried to rear on our own mulberry leaves. By Thursday morning it was clear that they had accepted this food (a mixture of black and white mulberry leaves), and to my eye the ones feeding on mulberry already looked larger and somehow healthier, dare I say ‘happier’ –what do you think?
If you have read the chapter on silkworms, or attended the lecture you will realise that silkworms are rather difficult to rear, and can catch all manner of diseases.
To try and stop this from happening I am making sure that I scrub and then disinfect all containers and equipment that I use in rearing, and I am trying to keep them at a hot enough temperature. At the moment I am rearing them at 24oC, when they are older this temperature can be reduced a bit, but should still be above 20oC. If the temperature is too low they become very sluggish, fail to feed, and are much more likely to die.
I shall report on their progress here, and you can always pop into the Wednesday practical over the next two weeks to see how they are growing.