It is almost two weeks since the silkworms arrived at Reading as first or early second instar larvae.
Silkworms on Monday 31st October feeding on mulberry. Most have just entered their fifth and final instar.
The larvae feeding on mulberry leaves are now entering the fifth and final instar, and some are over 5 cm long and about 7mm in diameter. I’m trying to rear them now at about 23C, which is a bit difficult as the rearing room, with assorted fridges and freezers, is not well ventilated and tends to build up heat. Still, I can keep the door open.
Some fifth instar silkworms on 31 October.
In the practical last week some people asked me what the moulted skin looks like, and I have a couple of photos below which shows this.
This silkworm has just moulted to the fifth instar, its moulted skin can be seen above it.
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Two skins from silkworm larvae that have just moulted into the fifth instar. You can see the outline of their prolegs and body segmentation. The large black lump to the left of the skin on the left is the remains of the gut contents: the larvae moult their gut lining and their gut has to be completely empty before moulting.
Unfortunately, the larvae feeding on artificial diet fared less well last week. Although I was careful to move them onto new food and sterilise the containers, many died. I moved some more on to mulberry leaves, and they seem to be growing now, but although some of the remainder on artificial diet were growing and had entered the fourth instar, most were not and seemed to die during moulting.
Silkworms feeding on artificial diet on 31 October. These are the same age as those above, but are much smaller. A dead one can be seen top left.
Thus, yesterday I decided to kill these larvae and preserve them while I still could, so that there are at least some demonstration silkworm larvae available in the coming years, if we cannot get live silkworms.
It will now be a race for the silkworms to complete growth before the mulberry leaves become unsuitable: yesterday there were not many leaves that were still green, and I picked most of them. Also, I will have to prepare the mountages for them to spin their cocoons.
Close-up of a fifth instar larva feeding on mulberry 31 October.