How many days does it take for silkworm eggs to hatch? Learn how to store them until next year and tell whether they are alive or dead

China is the first country in the world to raise silkworms and produce silk fabrics; its origins date back to the Yellow Emperor period, with more than 4,000 years of history. A silkworm's life goes through four different stages: egg, larva, pupa and adult. So how many days does it take for silkworm eggs to hatch? How do you store them until next year? How do you tell whether silkworm eggs are alive or dead?

How many days does it take for silkworm eggs to hatch?

It takes about 15-30 days for silkworms to hatch from their eggs. Silkworm eggs are generally kept in the refrigerator; after they are taken out and placed at room temperature, the temperature best suited for silkworm egg hatching is about room temperature 25°C. The eggs gradually turn purplish black, and after about two weeks or so, larvae can hatch out. After the larva bites through the eggshell, it first pokes out its head, then crawls out of the eggshell.

Silkworms reproduce by eggs. Silkworm eggs look very much like fine sesame seeds, about 1 mm wide and about 0.5 mm thick. One female moth can lay 400-500 silkworm eggs. 1700-2000 silkworm eggs weigh about 1 gram, with a diameter of 0,.2cm. As for the color of silkworm eggs, when just laid they are pale yellow or yellow; after 1-2 days they become pale red bean color or red bean color; after another 3-4 days they turn grayish green or purple, and then no longer change, which is called the fixed color. The outer layer of the silkworm egg is a hard eggshell, and inside are yolk and serosa. The embryo in the fertilized egg continuously absorbs nutrients during development and gradually develops into an ant silkworm. It crawls out of the eggshell, and after the eggshell is empty it becomes white or pale yellow.

The larva just hatched from the silkworm egg is called a first-instar silkworm. After eating mulberry leaves for about 3 days, it begins the first molt, molting for about 1 day; after the first molt it becomes a second-instar silkworm. The second instar lasts about two and a half days, then begins the second molt, molting for about 1 day; after the second molt it becomes a third-instar silkworm. The third instar lasts about 3 and a half days, then begins the third molt, molting for about 1 day; after the third molt it becomes a fourth-instar silkworm. The fourth instar lasts about 4 days, then begins the fourth molt, molting for about two days; after the fourth molt it becomes a fifth-instar silkworm. The fifth instar lasts about 6-8 days. Before spinning the cocoon it stops eating mulberry leaves, and the silkworm body contracts and becomes semi-transparent, which is called a mature silkworm. Usually first- to third-instar silkworms are also called small silkworms, and fourth- and fifth-instar silkworms are called large silkworms.

How do you tell whether silkworm eggs are alive or dead?

When silkworm moths lay eggs, there are three situations.

1. Those that turn brown or a darker color in two or three days are diapause eggs that will hatch next year.

2. Those that do not change color for several days, or turn pink or red and roughly on the 8th day show blue dots, and then hatch ant silkworms, are non-diapause eggs.

3. Those that never change color and later shrivel are unfertilized eggs, that is, dead eggs.

How do you store silkworm eggs until next year?

The storage of diapause eggs is divided into room-temperature storage and refrigerated storage. The refrigeration here is not freezing; if placed at below-zero temperatures, it will cause all of them to die.

1. Refrigerated storage

The method of refrigerated storage is, 10 days after egg laying, after confirming that the silkworm eggs have turned a dark color and entered diapause, to put the silkworm eggs into a refrigerator at 5°C for cold storage. Disposable lunch boxes or plastic bags can be used to store the silkworm eggs.

The issue to note with refrigerated storage in a refrigerator is that the silkworm eggs must be kept dry and must not have water droplets; they also must not be placed in the cooling area, to prevent freezing.

Generally speaking, after storage for 100-120 days, the silkworm eggs have basically exited diapause. Although the two-day hatching rate may not reach commercial standards, it is still enough for home silkworm rearing. If the time is less than 3 months, it is better not to take them out, as the hatching rate will be especially low. But refrigeration should also not be too long; after more than half a year, the hatching rate will also gradually decrease.

If eggs laid in the first half of the year are to be stored until the second year for rearing, you can consider storing them at room temperature for the first part of the time, so that the silkworm eggs have not gone through a simulated winter and the possibility of embryonic development is relatively low, then put them into the refrigerator around the end of the year, roughly between October and December. The next spring, when the mulberry leaves sprout, the silkworm eggs can be taken out to hatch.

For example, the picture below shows the poster's silkworm eggs from August last year. They had been kept at room temperature before, were put into the refrigerator around November, taken out at the end of March, and hatched in the last two days.

2. Room-temperature storage

Room-temperature storage is also an effective way to store silkworm eggs; if stored well, they can also be kept for a long time.

Generally speaking, room-temperature storage requires attention to temperature control and light-shaded storage. Just place the silkworm eggs in a cool place and leave them still, such as a cool basement or a shoe box under the bed. Remember: no light! No light! No light! For silkworm eggs kept at room temperature for more than half a year, once they are exposed to light, they will hatch one after another, and the consequences will be serious.

The season for raising silkworms

Spring and summer should roughly match the growth cycle of mulberry trees, to ensure an adequate supply of mulberry leaves.

Silkworm rearing methods

1. Rearing method: fourth- and fifth-instar silkworms are in the large-silkworm stage. The suitable growth temperature is 25°C. Silkworms have weak resistance to high temperature, high humidity and carbon dioxide, eat a large amount of mulberry leaves and produce a lot of excrement, so indoor floor rearing and outdoor frame rearing can be used.

2. After receiving the silkworm eggs, protect them in a suitable environment so that the embryo develops normally. The specific method is: in a disinfected silkworm room, spread the silkworm eggs flat in a silkworm tray with the egg surface facing up. For days 1—4, the room temperature is required to be 24°C, with a wet-dry difference of 2—2.5°C; for days 5—10, the room temperature is required to be 27°C, with a wet-dry difference of 1.5—2°C. When the embryo develops to the later stage and a small number of silkworm eggs are found to show small blue dots, immediately cover the silkworm eggs with black cloth to darken them. After about 40 hours, that is, at 4—5 o'clock before dawn on the third day, remove the black cloth, wrap the silkworm eggs in white paper with the egg surface facing up, turn on the light for exposure, and let the ant silkworms bite through the eggshells and hatch out.

3. The main technical measures for rearing large silkworms are:

(1) Improve the environment and do a good job of ventilation to prevent stuffiness.

(2) Build a shed for shade to prevent hot air from entering the silkworm room.

(3) Spread the silkworm bed sparsely, place it low, and feed frequently in small amounts.

(4) Do a good job of mulberry garden management to ensure the quantity and quality of mulberry leaves during the fifth instar, so that the silkworms eat their fill and eat well, and prevent the silkworms from eating old hard leaves, overly tender leaves, nutrient-deficient leaves and leaves lacking water.

Details to note when raising silkworms

1. Remove the sand before molting. This is to avoid excessive accumulation of silkworm droppings, where pathogens can easily breed and spread, and then invade the silkworm body during the molting period.

2. During molting, silkworms do not eat or move, and mainly rely on the nutrients absorbed from eating mulberry leaves before molting to maintain life activities. So they must be fully fed before molting. If mulberry leaf feeding is stopped too early, it will cause hungry molting, and silkworms that molt hungry have weak constitutions, poor resistance and are prone to illness.

3. During molting, silkworms have weak resistance to various external disturbances, so attention must be paid to protection during molting.

When 95% of the silkworms have settled into molting, sprinkle fresh lime powder and the silkworm medicine “Disease Prevention No. 1” to prevent pathogens from invading. If a small number of silkworms neither eat mulberry leaves nor molt, it is because they have not found a place to settle into molting. At this time, put out some mulberry leaves and pick out the green ones to molt in batches.

4. Silkworms are poikilothermic animals, with an adaptive range of 20-30°C. The spring silkworm period often encounters low-temperature and high-humidity weather, and the focus is on adding warmth and removing moisture. The summer silkworm period is high-temperature and high-humidity, and the focus is on cooling and removing moisture, keeping the air in the silkworm room circulating and eliminating stuffiness. If the autumn silkworm period encounters high temperature and dryness, then moisture must be added indoors, combined with disinfection, that is, use fresh lime powder and bleaching powder mixed with water to spray the floor and walls; you can also hang thoroughly wet cloth on the silkworm racks to keep the silkworm room moist and avoid difficulty in molting and half-molting in silkworms.