Silkworm Rearing Guide
- using Silkworm Chow as the food source
SILKWORMS are the larva of the silk moth (bombyx mori), this guide promotes a simple method of rearing silkworm larvae. There are a few underlying essentials, ensure that they are cleaned regularly, that you meet their heating and humidity requirements through every instar and ensuring that they are fed often enough are pretty much the main factors of silkworm larval rearing. I have tried to note these key points where needed, with other pointers to look out for along the way. Silkworm rearing is about finding the most effective and least time consuming method that works for you.
In this guide, I mention the silkworms “instars”, instars are the name given to the stage of larval rearing following each moult that the larva go through, all in all silkworm larvae moult their skin four times during the larval period, going through a total of 5 instars.
There are many tried and tested methods of silkworm rearing, this guide is based on the use of mulberry chow for feeding as many are unable to source large amounts of fresh mulberry leaves (they eat ridiculous amounts of food! In total, their growth throughout the larval stages from the first instar through to the spinning stage is immense, they grow 10,000 times their initial size in fact!!).
An essential factor to healthy silkworms is the cleanliness of their environment, remove their frass (silkworm poop) regularly to prevent the build up of mould (one of the biggest killers in silkworm rearing!), ensuring that their containers are never too condensed etc. It must be remembered that young silkworm larvae are very delicate, especially at the younger stages of silkworm larval rearing, so extreme care must be taken at all times, if you are transferring small larvae use a soft paintbrush (can you see the tiny little guy below?).
Please note – Whilst helpful an incubator is not essential to the rearing of silkworms – especially in the warmer parts of Australia
If you are concerned about humidity and are not using an incubator you can increase humidity by placing a small damp piece of paper towel in with your eggs – Ensure that it does not contact the eggs directly and that no water collects in the container – it is also essential that you allow fresh air to reach the eggs twice daily and keep an eye out for mould.
Generally after the first few eggs begin to hatch you will find that it takes around 2 days for all of the larvae to hatch out, do not feed the larvae on the first day that you notice hatching, wait 24 hours from this time, this is long enough to ensure that the fertile eggs have hatched without depriving the first hatchers of their feed. If the first hatchers are fed to early, the moist mulberry food on the eggs that haven’t yet hatched, may prevent them from hatching at all.!
One way to synchronize hatching, when you see that the eggs have begun to lighten in colour, we know that the larvae are nearly ready to hatch, put the eggs in complete darkness for 1 day (still within the same heated conditions). The following day, remove the eggs from darkness and place in the light (not under direct sunlight, this can be too hot for them!), this way you will find that they should all hatch at the same time (within a few hours).
First feed.
Once the larvae are ready for their first feed, place a small amount of insect mesh over the top of the young larvae and grate some of the mulberry chow over them (not a large amount of food as the weight of the mesh may squash them). You will find that the larvae will begin to climb through the mesh and onto the chow. After a few hours and most of the larvae have transferred onto the food, remove the mesh from the container and place it in a new disinfected container. If any silkworms remain, use a very fine paint brush to transfer the remaining larvae into the new container, making sure that you are very careful as the young larvae are very delicate.
The second day of their first instar, check their condition, remove any desiccated chow and grate new food over them. When checking silkworms daily if you find that several hours after a feed they have eaten all of the food that you gave them, feed them again, their appetite seems to never end..!
The same procedure should be applied on the third day, ensure that desiccated diet is replaced. At this point you should now find that the larvae are white/grey in colour and are now clearly visible on the diet.
The fourth day of larval rearing you will notice that the larvae have begun their first moulting period. Their bodies are translucent and they become to fix to the substrate with silk threads. Again, replacement chow should be added if the existing chow is very dry (in this case a very small quantity). The fifth day you will see that the majority of larvae are moulting. Some of them have already moulted and have big light heads (shown in red) some of them are still undergoing the moulting process and are darker in appearance and still have a smaller head (shown in yellow).
The sixth day the majority of larvae will have moulted, you can fully distinguish the black shiny large head, the opaque body, greyish in colour (below, circled in red). Larvae still moulting are reddish-brown and still translucent, and their head capsule is comparatively small (below, in yellow). Silk threads should be clearly visible on the food. Now it is time to give them food again, but before you do so, place a layer of mesh over the larvae. Slice thin strips of the chow over the mesh and leave the silkworms to climb onto it and begin feeding (this should take around 3 hours). Please note that the larvae will climb very quickly onto the new food, only if the old food is completely desiccated. If old chow remains, ensure that this is removed from the container, if you leave the old food in their container when putting new food on top, it becomes a breeding ground for mould..!
The following day is the second day of the second instar, if their food has been eaten then replace with new thin slices of the chow, ensuring that any old chow has been removed.
The third day of the second instar the larvae will have begun moulting again as the second instar is the shortest. On this day the container lid must be removed and the larvae must not be fed in order to let the existing chow dry out.
The day after this place new netting over the larvae and give them another feed of thinly sliced mulberry chow. Again, the larvae climb through the mesh themselves after 2-3 hours, now they can be easily transferred again to a new, clean container. Place the lid on their container ensuring that there is ventilation, temperature is now increased to 80f and humidity levels of 75%. This is the first day of the third instar.
The third day, new thin slices of chow should be placed where the existing has been eaten or desiccated. Ensure removal of any old/dry chow.
On the fourth day of the third instar, larvae are beginning moulting for the following instar. Do not feed at this point as they will not eat. at this stage of their development is easier to distinguish, also their old skin can be seen in their container (circled in red).
The second and third day of the fourth instar, again, new diet should replace any of the existing if it has dried out. Cleaning at this stage is suggested by laying new mesh on top of the larvae, feeding and transferring into their box after any frass has been removed.
On the fifth day of the fourth instar, larvae will be moulting again. New chow must not be added in the box, and the container that hold the larvae should have its lid removed in order to permit complete desiccation of the chow, humidity here should be reduced to 60%.
In the picture below you can see circled in red, the skin residue that is left behind after this moult, almost looks like the dried remains of a silkworm.
Larvae should now be transferred to a new, clean container, temperature adjusted around 77f and humidity around 65%. This is the first day of the last instar.
The last instar moulting is longer than other moults (around 48 hours). If there are remaining larvae after this period that are on the old food still moulting, you can leave them without a lid on their container for the following day, when they are ready to begin the last instar, continue to rear them in the same manner as the larvae that moulted on the previous day (generally they are in a minority (around 5%), only if the rearing is not homogenous).
The second day of the last instar.
Cleaning is very important during the last instar (as you can see below , the amount of faeces following a feed), the larvae should be cleaned daily, via use of mesh, tweezers or by hand (while wearing clean gloves). Their waste should be removed from the container, and the container to be cleaned.
The same procedure for the fourth and fifth days of the last instar.
The sixth and seven days of the last instar you will find that the larvae begin to excrete uric acid from their gut, they release this in preparation for spinning their cocoon, this however causes high levels of humidity and therefore spinning larvae should be removed from the environment when spotted and put in a separate container for spinning. A small amount of chow should be given here to allow those still feeding to continue. Ensure that the lid is removed from their container at this point to lower the humidity (needs to be around 60%)
Mature larvae that are ready to spin can be distinguished by the change in their appearance, they become translucent to look at and begin to shrink slightly due to the excretion of uric acid, identifiable as below.
Mature larvae that are ready to spin can be identified by several indications, the excretion of uric acid, their ‘heart line’ which is the long pulsating line that runs along the dorsal (upper) part of their body (part of their circulatory system), these are sure signs that a larva is nearing pupation.
Males are generally smaller then females, most males you will find to be moving around like a headless chicken, in search for a mate.
