Aussie Fauna Promoting Education and Pet Nutrition through silkworms
Silkworms have played an important role in teaching us the cycle of life. The mention of silkworms often evokes childhood memories back to primary school days, raising these caterpillars in shoe boxes and raiding the neighbour’s Mulberry tree in an attempt to satiate their never ending appetites.
Silkworms are tiny (about the size of the “i” in tiny) when they hatch from their eggs and within four weeks grow to over 10,000 times in size. Other than maintaining a constant temperature and sourcing food (mulberry leaves or silkworm chow) very little equipment is required to rear silkworms – remember the shoebox! Once the worms are set up, have a constant supply of food and a clean environment, the silkworms grow very quickly.
Traditionally, a steady supply of mulberry leaves was required to grow and rear silkworms. A mulberry based food, often referred to as “silkworm chow” is now available which allows silkworms to be raised anywhere, year round; access to a mulberry tree/leaves is no longer required.
Environment and hygiene
It is important to thoroughly wash your hands with soap and water before handling the food or silkworms to prevent contaminating their environment with unwanted “bugs.”
Silkworms are best maintained at temperature over 22°C (ideally 24°-27°C).
Being clean is the key to successful silkworm rearing. Silkworms eat a lot and as a result poo a lot; keeping their container clean is very important. Mold and bacteria love to grow on old moist chow, mulberry leaves and frass (silkworm poo) so it is important to clean out old food and frass daily and transfer them to a new clean container often.
To easily transfer the worms to a new container, put a plastic net (cheap plastic gutter guard works well) on the larvae and then put fresh chow or leaves on the net (see Figure 1.). Leave it there for several hours and the worms will climb through the net onto the new food. Please note, larvae will climb very quickly on the new chow only if the old chow is completely dried. At this point, you can transfer the larvae by lifting the net out of the old container and placing it into the new clean container.
Figure 1. Use of a plastic mesh to transfer silkworms to a new clean container.
Four to five weeks after hatching and near constant eating, the silkworms are ready for the next step in their life cycle - to spin their cocoons. They would have gone through five different instar stages, and moult between each instar. Prior to moulting they will take a break from eating and raise their head in the air and appear as if they are praying – it is best to not disturb them at this time.
When silkworms are ready to spin, their appearance changes and they begin to look more translucent, begin to shrink in size, and pass larger, wetter stools. They will begin to go walk-about and leave their food looking for the ideal location to build their home. Take advantage of objects around the classroom – i.e., the cardboard tube from finished toilet paper rolls are perfect scaffolding required for the silkworm to spin their cocoon. After a day or two, the spinning process will be complete and the silkworm will moult one last time into a pupa. You should now remove the excess silk, or floss, around the cocoon. Flossing will prevent the moths from getting entangled when they emerge from their cocoon ten to fourteen days later.
Moths and Reproduction
Once the moths emerge, their sole mission is to breed and lay eggs. They cannot fly, do not eat, and they do not drink. Females are larger than the males and have very round abdomens which are full of yellow unfertilized eggs. Males will franticly flap their wings and spin in circles once they sense the presence of a female; flapping continues until they meet and the male attaches to the female. Most pairs typically copulate for over 12 hours.
Males are persistent and if given the chance will attempt to continuously mate. In order to let the female lay her eggs, separate the pair and place the females in a separate container, a paper lined container is ideal for her to lay her eggs on. She will lay between 100-400 yellow eggs. If the eggs are fertilized, over the next few days the eggs will change from yellow to black. If they are not fertile they will remain yellow.
Seal the eggs in a plastic zip lock bag and place into the refrigerator for a minimum of three months. The vast majority of silkworm strains in Australia are univoltines – meaning they produce only one generation per year. The eggs of univoltines remain in diapause, or dormant, until the next spring. In order to continue breeding silkworms, the eggs must be “wintered”. Eggs can be stored in the refrigerator for up to 18 months.
After the minimum of three months in the refrigerator (the silkworm eggs in your Classroom Kit have already been “wintered”), simply place the eggs into a plastic container (all of our eggs and kits come with a petri dish to hatch the eggs in), and warm them up to over 22°C (ideally 24°-27°C) and provide 12 hours light/12 houra dark photoperiod.
Keeping the container in an incubator is ideal however homemade incubators can be made. Other warm areas that can be used include placing the container near a heat source such as room heaters or pet reptile enclosures (do not place directly on top of the heat source as this will be too hot for the eggs and may kill them). In most parts of Australia, ambient humidity is sufficient for the eggs to hatch. In arid locations, place a small piece of damp paper towel (or sponge) in the container, do not allow the eggs to contact the damp paper towel. Generally the eggs will hatch between 10-12 days after they are removed from the refrigerator. The eggs will change from a dark purplish colour to a light bluish/gray colour a couple days before they hatch.
Feeding newly hatched silkworms
When the eggs begin to hatch, provide young mulberry leaves or prepare cooked mulberry chow. All worms must be fed within 24 hours after hatching or they will starve, so be sure to feed the early hatchers. Sometimes the hatchling silkworms (known as kego) may not find their first meal; if this is the case a fine paint brush can be used to carefully place the silkworms onto the food for their first feed. The petri dish is the perfect container size for new hatchlings, food is never too far away.
Fresh leaves or chow need to be offered a couple of times a day and humidity maintenance is crucial to rearing kego. Preventing condensation build up is mandatory as too much moisture with drown the small silkworms, on the other hand if it is to dry the food desiccates quickly and the kego will not be able to eat. Many factors will affect the humidity including food quantity provided, container size, temperature, ambient humidity. Once the right balance is found, the kego will grow very quickly!