10 Ways to Breed Silkworms

How do you get silkworm eggs?

You can order eggs online. They're available at any time of year. You can order breeds with different patterns or that make different colored cocoons, but they're all raised in basically the same way. The eggs start out at tiny, yellow dots. By the time they get to you, they'll probably be gray-green, gray-purple, or light brown. If you see a different color, you might have eggs with a rare mutation! The silkworm is a domesticated species that doesn't exist in the wild. If you see its wild relatives on mulberry trees in East Asia, leave them on the tree—they can't be bred the same way.

Where should you keep silkworm eggs?

Keep the eggs in a small container in a warm, well-lit room. A petri dish or a shoebox are common choices. The eggs will hatch fastest at around 29ºC (84ºF), but they'll eventually hatch at room temperature too. Careful—they like a warm room, but direct sunlight is too much heat. The eggs don't do well if they're super dry or super moist. If the room is dry, try adding a little square of damp paper to the container, but not touching the eggs. If the container is damp enough that drops form on the sides, move it somewhere drier.

How long do silkworm eggs take to hatch?

About one to three weeks depending on temperature. If the temperature is perfect (about 29ºC / 84ºF), the eggs can hatch in as little as nine days. At room temperature, your eggs might take up to three weeks. It's normal for some eggs to fail to hatch. Blue eggs that fail to hatch might be a sign that the eggs weren't handled right, so try ordering from a different supplier next time. (But some blue eggs can still hatch, so don't give up them.)

Eggs can also keep overwinter in a warm fridge. Many silkworms only reproduce once a year, and their eggs do best when they stay dormant until the next spring. If you successfully breed the silkworms, it's usually best to keep the new generation of eggs in the refrigerator until next spring. Keep the fridge temperature above 10ºC (50ºF) to avoid killing the eggs. This temperature is higher than the standard food-safe fridge temperature, so use a separate mini-fridge If your silk worm breed was labeled "bivoltine," "polyvoltine," or with a number 100 or above, you could try to breed multiple generations per year, between spring and fall. Even then, the breeding schedule isn't guaranteed, since it's affected by heat and light.

What's the best place to keep silkworm larvae?

Keep them in a warm container with paper towels and holes for air. Your silkworms can live their whole lives in a shoebox about 6 inches (15 cm) deep. Just poke plenty of holes in the lid for air, and line the container with paper towels. A plastic or glass container is a bit worse than cardboard, because it's harder to get airflow and can overheat more easily. Silkworms love a warm (but not hot) home: always keep them above 20ºC (68ºF), and ideally around 27ºC (81ºF). Newly hatched silkworm larvae are tiny squiggles. If you hatched the eggs in a petri dish, you can catch the squiggles on the end of a fine tip paintbrush to move them. It's also fine to put the whole petri dish in the box. The larvae start out very small, so one container to start with is fine. If they start to get overcrowded as they grow, move some to a second container. Giving the silkworm larvae indirect sunlight during the day is nice if you can manage it. Silkworm larvae do react to light, and will feed more if they have light during the day and darkness at night. That said, the silkworms won't die if you keep them in the dark. Just be careful not to put the container in direct sunlight, which can overheat them.

How do you feed silkworm larvae?

Mulberry leaves are best, but not available year-round. You'll need two types of leaves. Thin, tender, young mulberry leaves are the only ones the youngest silkworms can eat. Thick, juicy, dark green leaves are better for older larvae. If you can't get the young leaves, use artificial food and switch to mature leaves later. Ask the people who sell the leaves whether good-quality leaves will be in season until at least 24 days after the eggs hatch. If not, it's better to use artificial food the whole time instead. Silkworms fed on mulberry leaves sometimes won't accept artificial food later.

You can order artificial food online instead. This should come with instructions that tell you how to prepare it before feeding your silkworms, and how much they eat. Food is the only way that silkworms get water, so make sure to replace it as soon as it dries out.

Wash the mulberry leaves before feeding. Leaves can carry diseases or pests. Wash them under running water, then shake dry and store them in the fridge in plastic bags. (A little damp is fine, but silkworms don't want soggy leaves.) Before each feeding, throw away any yellow or dried up leaves. It's even better to go the extra mile and disinfect them. To do this, add 3 tablespoons (44 mL) of bleach and a drop of dishwashing detergent to 1 gallon (3.8 L) of water. Soak the leaves for three minutes, then rinse them very thoroughly under running water. (Any soap left can kill the larvae.) Shake dry and store in plastic bags in the fridge.

Start with one leaf a day, then increase as they grow. Wrap the stem of a mulberry leaf in a scrap of moist paper towel and put it in the container. Replace this at least once a day. After a few days, start putting in several leaves bunched together instead. Use enough leaves (or replace them often enough) that the silkworms always have access to fresh food. For the first couple days, use a soft paintbrush to very gently pick up the tiny, newly hatched larvae and move them off of the old leaf, then onto the new one. If the newly hatched larvae aren't eating, the leaves might be too thick. Try slicing them as thinly as you can and sprinkling them into the container, or switch to artificial food.

How do you clean the silkworm habitat?

Brush out the feces, old food, and skin molts every other day. Leaving it in there too long can cause mold or bacteria to grow. For the first few days, when the larvae are tiny, you can use a small paintbrush or a small spoon to clean around them. Once they're larger, you can pick them up and move them to a temporary box while you clean. It's best to leave the larvae alone while they molt. In each molt, they rest for about a day, staying still with their head held up before shedding their skin. Let them snooze and come back to clean tomorrow! Don't wash with water and especially not soap, which can kill the larvae. The life cycle is only a few weeks long, so you can wait until they're in cocoons before you do a thorough clean.

How do you get the silkworms to cocoon?

Put in sections of toilet paper roll when the larvae turn translucent. Silkworm larvae usually molt four times, then spend a final six or seven days feeding before they're ready to make a cocoon. Their bodies then turn a little translucent, and they stop eating. When they roam around and keep raising their heads up, they are looking for a place to spin cocoons. Help them out with a cardboard toilet paper roll cut into circles, or move them into rolled-up paper towels or newspaper and twist the ends closed. If some of the silkworms have already started to spin silk, leave those ones alone. Interrupting the spinning can kill them.

The transformation into moths takes 8 to 14 days. This doesn't include the two or three days it takes to finish spinning the cocoon. Leave the cocoons undisturbed to give the silkworms the best chance to turn into healthy adults. After two or three days of spinning, the silkworm inside spends another two or three days pupating. After this point, you can cut open the end of a cocoon with a razor blade, and gently pull out the pupa (for instance, to show them to a science class). If you are very careful and return the pupa to the cocoon, it can still become a moth. The moths usually come out in the early morning, so start waking up early if you want to be there when it happens.

How do silkworms mate?

Silkworms mate as adult moths, right out of the cocoon. You can tell the sexes apart by their size (females are larger) and behavior (males move faster and flutter their wings more). While mating, they face away from each other and join the ends of their bodies. After mating, the female lays hundreds of eggs.

Do I need to look after the silkworm moths?

The moths don't need food or any other care. Adult moths can't eat and only live for between 3 and 10 days. All that's left to do is appreciate them while they're still around. Silkworm moths can't fly, so you can take off the lid to look at them without much risk of them escaping.

Can I cross-breed different types of silkworms?

Yes, you can cross-breed to make new strains. Silkworms of different strains will mate with each other, and their children might look different or make different sizes or colors of cocoons. Keep in mind that cross-breeding silkworms for a specific purpose (like larger cocoons or healthier larvae) takes a lot of training and experience. If you want to experiment, it's usually more consistent to cross-breed in spring. If you can, separate the sexes so you can combine the males of one strain with the females of another. (The male larvae are usually bigger and can have different markings, but it's hard to tell in some strains.)