Silkworms are low-maintenance insects, but they do have specific needs at each stage of their roughly six-week life cycle. Getting the feeding schedule, humidity, and cleanliness right makes the difference between healthy worms that spin plump cocoons and a tray full of problems. Here’s what to do from the moment your eggs arrive through the adult moth stage.
Understanding the Life Cycle
Silkworms (Bombyx mori) move through four distinct stages: egg, larva, pupa, and moth. Eggs hatch in 9 to 10 days under the right conditions. The larval stage, where all the eating and growing happens, lasts 24 to 28 days and includes five growth phases separated by four molts. When a larva is ready, it spins a silk cocoon over 3 to 4 days, then spends another 8 to 10 days as a pupa inside before emerging as a moth. Adult moths live only 3 to 6 days, during which they mate and lay eggs but never eat.
Knowing this timeline helps you plan. The larval stage is the most labor-intensive part, demanding daily feeding and cleaning. Everything before and after is relatively hands-off.
Hatching Silkworm Eggs
Keep eggs at 23°C to 25°C (73°F to 77°F) in a dimly lit spot. Bright or direct light can disrupt embryo development and lower your hatch rate. A room-temperature closet or a shelf away from windows works well. Spread eggs in a single layer on a sheet of wax paper or parchment inside a shallow tray so the tiny hatchlings don’t pile up.
You’ll see the eggs darken from pale yellow to a blue-gray color a day or two before hatching. Have fresh food ready, because newly hatched silkworms are smaller than a grain of rice and need to start eating almost immediately. Use a soft paintbrush or feather to gently transfer hatchlings onto their first leaves or food.
Feeding: Mulberry Leaves vs. Artificial Chow
Fresh mulberry leaves are the natural and ideal food. They’re about 80% water and rich in protein, carbohydrates, vitamins, and minerals. Young silkworms do best on tender, freshly picked leaves. Older worms can handle tougher, mature leaves. Wash leaves and pat them dry before feeding to remove any pesticide residue or surface contaminants.
During the later larval stages (fourth and fifth instars), silkworms are eating machines. Research on feeding frequency shows that three to four feedings per day produces the best cocoon results. For smaller home setups, feeding three times a day at roughly eight-hour intervals is a practical target. In the first few instars, when the worms are tiny and eat little, two feedings a day is usually enough.
If you don’t have access to a mulberry tree, commercially available silkworm chow is a reliable alternative. It comes as a powder that you mix with water and cook. For a half-pound packet, combine the powder with 3 cups of hot water using a hand mixer until smooth, then microwave covered on high for about 8 minutes (in a 1200-watt microwave) until it boils. Let it cool, then refrigerate. It firms to a soft, cheese-like texture that you grate over your worms. Keep it covered in the fridge to prevent drying out. A stovetop method works too: bring the same mixture to a boil for about 5 minutes, stirring constantly to avoid scorching.
Replace uneaten food before it dries out or starts to mold. Silkworms won’t eat dried-up leaves or spoiled chow.
Housing and Ventilation
A simple plastic bin, shoe box, or shallow tray works for a small batch of silkworms. The container doesn’t need to be tall since silkworms don’t climb much, but it should be wide enough that they aren’t crowded on top of each other. As the worms grow, you’ll likely need to split them across multiple containers.
Good airflow matters. Stale, humid air breeds mold and disease. If you’re using a plastic bin, poke ventilation holes in the lid or use a mesh cover. Avoid airtight enclosures. At the same time, don’t place containers in a drafty spot or near a fan blowing directly on them, especially during molting.
Line the bottom of your container with paper (newspaper or parchment) for easy cleanup. Younger worms can be kept on wax-coated paper, which resists moisture better.
Temperature and Humidity
Silkworms thrive at around 25°C to 28°C (77°F to 82°F) with roughly 70% relative humidity. This range produces the best larval weight, survival rates, and cocoon quality. Temperatures below 20°C slow growth significantly, and anything above 32°C can be lethal.
In dry climates or air-conditioned rooms, you can boost humidity by placing a damp cloth or shallow dish of water near the rearing container. In overly humid environments, increase ventilation to prevent condensation inside the bin. A cheap hygrometer placed near your setup takes the guesswork out of monitoring.
Cleaning and Disease Prevention
Silkworm frass (droppings) and leftover leaf fragments build up quickly, especially in the later instars when the worms are large. Dirty bedding is the fastest route to bacterial and fungal infections. During the first and second instars, clean the bed once per molt cycle. By the third instar, clean two or three times during that stage. In the fourth and fifth instars, clean daily.
The easiest cleaning method is to lay a sheet of netting or mesh over the existing bed, place fresh food on top, and wait for the worms to crawl up through the mesh to eat. Then lift the net with the worms and food, discard the old bedding, lay down fresh paper, and set the worms back down. This avoids handling the worms directly, which reduces stress and injury.
Wash your hands before handling worms or their food. If you notice any larvae that appear discolored, limp, or abnormally small, separate them immediately. Disease spreads fast in a crowded tray.
Handling Molts
Silkworms molt four times during the larval stage, shedding their skin to accommodate their growing body. You’ll know a molt is coming when worms stop eating, become less active, and raise their heads in a still, upright posture. Their skin may look slightly more translucent than usual.
During a molt, leave them alone. Stop feeding, avoid moving the container, and minimize vibrations and loud noises nearby. Keep conditions stable at 24°C to 27°C (75°F to 80°F) with humidity around 70 to 75%. A molt typically takes about a day.
After the molt, resume feeding gradually. Start with tender, high-quality leaves rather than tough ones. The freshly molted worms have soft new skin and are more vulnerable. Remove the shed skins gently to keep the bed clean, but try not to jostle recently molted larvae. Watch closely for any worms that seem to have had an incomplete molt or appear stressed, as problems during this window often show up in the hours right after.
Spinning and Cocoon Care
When fifth-instar silkworms are ready to spin, they stop eating, shrink slightly, and become translucent with a yellowish tint. They’ll start wandering, looking for a spot to anchor their silk. Provide a structure for them to spin on: crumpled paper, egg cartons, toilet paper rolls, or small cardboard dividers all work. Commercial setups use rotating frames called mountages, but anything with nooks and corners will do.
Keep ventilation high during this phase to help remove excess moisture from the fresh cocoons. Cocoon formation takes 3 to 4 days. Once complete, the pupa inside will develop for another 8 to 10 days before the moth is ready to emerge.
If you want to harvest the silk, you’ll need to process cocoons before the moth emerges, since the moth breaks through the continuous silk filament on its way out. If you’re raising silkworms as pets, feeders, or for breeding, simply leave the cocoons undisturbed in a warm, ventilated area and wait.
Adult Moth Stage
Adult silkworm moths emerge by softening one end of the cocoon with a secretion and pushing through. They have small, white wings but cannot fly, a result of thousands of years of domestication. They also have no functional mouthparts and do not eat or drink. Their sole purpose is to reproduce.
Moths live only 3 to 6 days. Males are smaller and will flutter their wings vigorously when they sense a female. Pairing happens quickly. After mating, separate the female and place her on a sheet of paper, where she’ll lay 200 to 500 tiny eggs over the next day or two. The eggs start out pale yellow and will darken if they’re fertilized.
If you plan to hatch the next generation, store the egg sheets in a cool, dry place. Many silkworm strains require a period of cold dormancy (refrigeration at around 5°C for several weeks) before they’ll hatch, mimicking winter. Others, called multivoltine strains, will hatch without a cold period. Check what type you have so you know whether to refrigerate or incubate right away.