Raising Silkworms

We have a lot of hungry mouths to feed around here, and as such we raise a variety of feeder insects. My personal favorite to raise – the silkworm.

Poor silkworms. Humans have been breeding them in captivity for over 4,000 years, and it is widely believed that the species (Bombyx Mori) are thought to be extinct in the wild! They’ve been raised in captivity for so long, that they have lost their ability to fly, as well as their natural immunity to disease and illnesses.

This lack of immunity has given silkworms a reputation for being difficult to raise. You must take precautions to ensure you do not introduce bacteria or contaminants to their enclosure or their food. I’ll go into more detail about this, below, but I have not found silkworms to be overly difficult. With a small daily time investment, your silkworm farm will do just fine.

Types of silkworms

There are many variations of silkworms, some have very distinct coloration and markings, while others may spin uniquely colored cocoons.  The most commonly raised silkworm is referred to as “normal,” which are simply white caterpillars.  We also raise Zebra, which are a mix of white caterpillars with black stripes, and Black silkworms, which are mostly black caterpillars with white stripes.  All three have the same nutritional value, but everyone knows that pretty food tastes better!

Why raise silkworms?

The most common reason why silkworms are farmed is for their silk. A few weeks after hatching from an egg, a silkworm will create a cocoon around itself in order to pupate, and eventually morph into a silk moth. This cocoon that is created is literally made of silk, so much silk, that if unraveled, a single cocoon would produce a single thread of silk that is half a mile long!  Unfortunately, in order to get the most usable silk, the freshly made cocoon is often baked or boiled in order to kill the pupa inside. This is done because when the moths emerge from the cocoon they release an iodine colored liquid, which softens the cocoon for exit, but in return damages the silk.

Silkworm pupa are a delicacy in some asian countries, where the pupa is removed from the cocoon and cook or fried in a variety of ways, none of which I would like to try. I do know a few chameleons that would love to try it, though.

Finally, silkworms and silk moths can also be raised as feeder insects for chickens, reptiles, amphibians, fish, and other birds. Silkworms are considered a very nutritious feeder, if not the most nutritious feeder insect, and can be fed as a staple food. They are soft bodied, high protein, low in fat with a high source of several key vitamins, including Calcium, Vitamin B, Iron, Magnesium, and Sodium.

Life Cycle

The life cycle of a silkworm is very similar to that of other caterpillars.  Silkworms start out as eggs that, in nature, would have been laid on the surface of Mulberry leaves in the spring or early summer.  After two weeks or so, and in ideal temperatures, the eggs would then hatch into tiny black caterpillars.  The Japanese call these newly hatched silkworms “Kego,” which roughly translates to “hairy baby.”  If you look very closely, you’ll understand where that name comes from!

A few days after hatching, the Kego will go through its first molt, emerging as a lighter colored and slightly larger larva.  The larva will molt (shed) once every 3-4 days during its life span, for a total of 5 molts.  The time between each of these molts is called an “instar,” and that is what is referred to when determining a silkworm’s age (ex: “the silkworm is in its 3rd instar, or approximately halfway through its life cycle”).

Once a silkworm has reached its 5th instar, approximately 4 weeks after hatching, it will begin to grow thicker and more plump.  Its skin will become more firm and their appetites will be ferocious!  The silkworm is preparing itself for the next stage of its life cycle, the pupal stage.

Now that the silkworm has reached its mature size, it will begin to look for a safe place to spin a cocoon and begin the pupal stage.  The silkworm can take one to three days to successfully spin a firm cocoon, within which it will begin its metamorphosis into a silk moth.  The pupa will stay within the cocoon for approximately two weeks, before emerging from the cocoon as a moth.

Moths emerge with one goal in mind – mating.  Immediately upon emergence from the cocoon, male silk moths will begin fluttering their wings in search of a mate.  When a female is found, the silk moths will “join” at their butts in order to fertilize the female’s eggs.  Mating moths will stay joined for 24+ hours.  Once separated, the female will immediately begin laying (gluing) her eggs down to begin the cycle once more.   After all of that work, a silk moth only lives for 3-5 days.

Getting Started

The first step to raising silkworms is to find a supplier of either silkworm eggs, or live silkworms.  My personal preference has been to order from either Coastal Silkworms, or Mori Feeders.  Both offer silkworm food (chow), eggs, and live silkworms.  Unless you have access to a large Mulberry tree, be sure to order food, as you’ll need it immediately upon hatching.

You’ll need to set up a hatching bin, or a larger bin if ordering live silkworms.  Let’s assume you are starting with eggs.  Eggs are typically shipped glued down to petri dishes, or glued to a small piece of paper.  The eggs are glued down for two reasons: to keep your new, expensive eggs from spilling all over the floor; and to assist newly hatching silkworms by holding the egg in place as they wiggle their way out.

I absolutely loathe using petri dishes for silkworms.  They are awkward to handle, easily dropped, and their lack of airflow encourages mold growth.  Mold is a silkworm killers – avoid it at all costs!  My preference is to use the cheapest plastic food storage containers I can find.  I prefer the sandwich sized containers from Target for the first few weeks of life.  Its also very handy to order or re-purpose inexpensive produce mesh bags, which are used in the “netting technique” which is explained later.

A common misconception is that you can refrigerate eggs that you don’t intend to hatch.  While this is true if you are harvesting and “over wintering” your own eggs, but you cannot refrigerate eggs that you have received from a vendor that were not already refrigerated and shipped on ice.  So unless you have a LOT of animals to feed, resist the urge to order those 2,000 eggs!

Hatching Eggs

Hatching silkworm eggs is easy peasy.  Take one of the cheap sandwich containers mentioned above and poke a few holes in the lid.  Nothing fancy, I just stabbed the lid a few times with a small sharp knife.  Newly hatched caterpillars wander a little bit, so the lid helps keep them contained.  If you are using petri dishes to hatch them you can get by without the holes, just open the lid every few days to allow some air to exchange.

Store your eggs in a dry room, preferably one of the warmer rooms in your home.  The eggs will hatch a bit quicker if kept closer to 75-80 degrees.  I keep mine in my bedroom, which is typically around 70-75 degrees in spring and summer.  Don’t keep them in the basement where it is likely too cool and too humid.  I have found that there is no need to invest in an incubator, I have had no problem hatching eggs at room temperature.  If your home is chilly, or its during the winter months, you can place your eggs next to (not touching or under) your reptile’s lighting, which will generally create ambient heat around the lights.

Hatchlings

Eggs typically hatch within two weeks, if temperatures are right.  In the wild, silkworm eggs would hatch in tune with the seasons, so if temperatures were too cold, the eggs would not hatching until the following spring to ensure the hatchlings would survive.  If you are hatching your own eggs, they likely would have needed to undergo an improvised winter season, which is discussed below.   If you purchased your eggs, they have likely already been “overwintered” and should otherwise hatch within 1-2 weeks.

Check on your eggs every morning and night.  It will be easy to tell when they begin to hatch as you will notice the eggs get slightly darker and more grey just before hatching, and then you’ll start to notice tiny little black caterpillars, hardly bigger than an eyelash.  Once you spot hatchlings, you’ll need to offer food within 24 hours or risk starving out the kegos.

Be sure to thoroughly wash your hands and utensils before touching the silkworms or their food.  I always keep a bottle of rubbing alcohol nearby and clean paper towels.  I’ll wipe off my forks/knives, my hands, etc, and lay my utensils on a clean paper towel.  Whenever I touch anything, such as the lid to the food, the refrigerator handle, the silkworm container, etc, I’ll grab my moistened paper towel and wipe my finger tips back off.  It is critical at this stage to keep everything clean and not introduce any more bacteria or germs to the kegos.  It sounds a bit intimidating, but in practice, its an easy habit to get into.  As the silkworms get a little older, they are a little less fragile, but you should always practice excellent hygiene when dealing with their food (which will be the first place that mold and bacteria grow).

To feed the hatchlings, offer the smallest slivers of prepared chow as possible.  Some people have good luck “shredding” the chow over a food grater, but my chow is too mushy to do that without creating  a lot of waste.  Instead, I use two forks and pick up tiny little pieces of food, which I then drop to the corners of the hatching container, away from the eggs.  Ideally, you’ll use the fruit netting I mentioned earlier, which will simplify the process of moving the silkworms later.  The netting technique boils down to laying a piece of netting (a small piece of produce net) down over the caterpillars.  You then lay your food on top of the net, allowing the silkworms will crawl up onto the netting to reach the new food.  In a day or two, when it is time to add new food, or to clean the container, you can simply lift the old netting out, or add another layer to move later.  More on that below… but that’s the technique I prefer.

If you don’t plan to use the netting technique, just be sure to spread the food away from the eggs.  The eggs will start to develop mold after a few days, so keep the worms and food away from that to prevent contamination.  After all the kegos have hatched, remove the eggs if possible.  If not possible, you’ll need to remove the kegos, instead.  To move the kegos, either use a net, or use a small, clean paintbrush to gently lift the food into a new container.  If there is any sign of mold, leave the old food behind.  You can also use the paintbrush to very gently lift the kegos themselves up and move them into the new container.  After moving the first 10 kegos, I guarantee you will be interested in trying the netting technique!

Now that you realize the net way is the right way, you can gently place the netting over the kegos.  Try to avoid touching the eggs if possible.  Putting a tiny spit-ball sized piece of paper towel on the eggs might help to keep the net from touching them.  We don’t want to take any eggs with us when we lift the net.   Then sprinkle tiny bits of food around the edges of the container, on the net.  Wait a few hours, and you’ll find that most of the kegos have climbed onto the food.  You can then lift the net and food out and into a new, clean container that is free of eggs. 

 

 

 

 

 

Always be sure to use the smallest chunks of food you can, at this stage, as you’ll want the food to be able to dry out to prevent mold.  You won’t be able to get every last kego over to the new food, so allowing the old food to dry out means you can add new food next to the old food without much risk, and without needing to handle the kegos.

Larval Stage

3 to 4 days after hatching, your tiny black kegos will go through their first molt.  You’ll know it when it happens, as they’ll more than double in size and develop a little bit more color.  They’re now in their 1st instar.  Congratulations, the hardest part is behind you!

You still need to be cautious with your baby silkworms, they are still tiny, fragile, and prone to illness.  Cleanliness is very important to the health of your silkies!  The easiest way to manage this, in my experience, is to keep your utensils and hands clean, and to prevent mold.  Now that you are out of the kego stage, your silkworms won’t wander much, typically only to the corner of the containers to molt.  I’d recommend taking the lid off the container at this point and leaving it off until they are ready to cocoon.  This will increase airflow as well as dry out old food and poop, which dramatically reduces the chances of developing mold.

If you were using petri dishes, at this point you want to move the silkies over to a larger container.  Use the netting technique, but avoid getting any eggs on the food or netting.  At this point you can begin offering slightly more food, but use a bit of trial and error to determine how much to offer.  You want to add just enough food that it will be eaten in a day or two, or that it will dry out after three or more days.  Dry food can easily be picked out of the container, or simply left in there with the new food placed nearby.  Efficiency is the game here, but you need to find the right balance to be both efficient and sanitary.

Two to three weeks after hatching, your larva will be about 1″ long.  At this size, I recommend using Gutter Guard from here on out.  Gutter Guard is a bit wider than fruit netting, but it is also more rigid.  It will serve the same purpose as an easy way to lift silkworms in and out for cleaning, but it also creates a bit of a barrier between the silkworms, their food, and their poop.  As the silkworms get larger, so does the size and amount of their poop.  You’ll need to empty the container at least every other day, as the larger poop does not dry out quite as quickly, but it sure does accumulate quickly!  Add new gutter guard and food when you start to notice a lot of silk and frass (poop) building up.  I like to place a soda bottle cap or a balled up piece of paper towel in bewteen the layers to keep them from touching, and to give the silkies enough space to crawl up onto the new netting.

The Pupal Stage

Four to five weeks after hatching, your larva will be ready to pupate.  The silkworms are usually around three inches long with a bit more girth to them.  As they near the pupal stage, you may notice a pulsating black vein down the silkworm’s back.  At this point, you may want to put a lid back on the enclosure, but be sure that there is excellent airflow.  You can either drill or cut lots of air holes in the lid, or even cut out a section and glue some Gutter Guard to the lid to create a screened vent.

There are a few tell tale signs that your silkworms are getting ready to spin, but not all silkworms will show these signs. 

• Silkworms need a place to be able to spin their cocoons without being disturbed, so you may find them wandering around the sides and walls of their container (why the lid is important at this stage).  
• The silkworm will spew a clear or murky liquid in order to “empty its guts” prior to pupating.  
• The silkworm may begin spinning silk from its mouth in order to start cocooning.
• You may notice a trail or chunk of silk on the walls of the container.

When these signs start to present themselves, you need to add something to the container that will offer a bit of privacy for the spinning silkworms.  If you disturb them while spinning, they may abandon that spot and look for a new one.  The problem with that is that they can only produce so much silk – so they will either not be able to form a proper cocoon, or they’ll simply die.  I prefer to move the silkworms that are ready into another, separate container, as the silkworms who are not ready to pupate are still eating and pooping like crazy.  Using another container cuts down on the mess, and prevents me from disturbing any silkworms that might be making their cocoon.  

I like to add toilet paper and paper towel cardboard inserts, but into 2 inch sections.  You can add the cardboard vertically, horizontally, or both.  Other great options include paper egg cartons, or even crunched up newspaper.  The silkworms will spread out and begin spinning their cocoons.  The spinning process usually takes a day, try to disturb or touch the container is little as possible for the best success.   Sometimes the silkworms wander into each other while spinning.  If they are just getting started, you can move the worm to another area, but sometimes they’ll spin themselves into the same cocoon.  We’ve had “twin” moths successfully emerge from a single cocoon!  We give the silkworm a day or two to finish up and harden their cocoons, and then we very gently detach the cocoons and move them into another bin with just paper towels lining the bottom.

The silkworms will remain in their cocoons for 2 – 3 weeks, at which time they begin their metamorphosis and transform into a pupa, or chrysalis, and eventually emerge as a moth.  It will shrink up and develop a hardened, brown outer shell.

The Moth Stage

After 2-3 weeks, moths will be ready to emerge from the cocoons.   The moth will spray an iodine colored liquid onto one end of the cocoon, which softens and disolves the cocoon and allows the moth to break through it.    The liquid does not always dissolve the cocoon and the moth may be trapped inside.  If you notice the brown liquid on your cocoon, but a moth doesn’t appear within 12 hours, you may need to careful cut the cocoon to free the moth.  We find that we have to assist them quite often.  

The moths have one thing on their mind… mating.  They no longer have a need to eat or poop, however, the females seem to release a light brown pheromone that attracts the males.  Males typically emerge fluttering their wings immediately looking for a mate.  You can easily differentiate male and female moths by their size.  Males are typically “normal” sized moths, whereas females are larger and usually quite round.  Males will sometimes have longer wings, however, it is not uncommon for both the male and female moths to have short, deformed wings.

The moths only live for 3-5 days, so they waste no time.  A successfully mating pair of silkworms will be joined at their butts for 24 hours or more.  I like to place a small Dixie Cup or container over the mating pair so that they are able to mate undisturbed, otherwise you’ll find other males trying to get in on the action.  After the mating pair separates, I place the cup over the female, who will immediately begin to lay her eggs.  Placing a cup over her will encourage her to lay her eggs in a tight group, instead of spreading them all over the container.  A few days after the eggs are laid, fertile eggs will begin to turn a darker color, whereas infertile eggs remain yellow or white.

In the summer, you may be able to hatch fertile eggs within two weeks at room temperature, however, most silkworm farmers prefer to simulate a winter season for the eggs by placing the fertilized eggs in a Ziploc bag in the refrigerator for 2-3 months.  Silkworms sync up with the season changes, and if temperatures aren’t perfect, the eggs will not hatch until the following spring.  Refrigerating the eggs tricks them into thinking that winter has come and gone, and spring has arrived.  You can store the eggs in the fridge for several months.  The longer they are refrigerated, the lower the hatch rate.  The eggs will hatch within two weeks once removed from the refrigerator.  The life cycle starts again!