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The return of the silk moth

As early as the 18th century, the Francke Foundations experimented with silkworm breeding. The Prussian King Frederick II hoped to avoid dependence on expensive imports from China by producing his own silk. With royal orders and a donation of 330 mulberry trees, silkworm breeding could be started in 1744 and raw silk could actually be produced. After initial successes, however, disease damage and adverse climatic conditions led to a collapse in yields, and in 1805 silk cultivation ceased altogether. 213 years later, in 2018, Cornelia Jäger succeeded in having silk moth caterpillars hatch again.

As part of the environmental education activities in the plant garden, children can experience the growth and transformation from egg to butterfly.

Two silkworm moth mating
Amore in the silk moth quarters! Two silk spinners have found each other. For several hours they will not leave each other.
Many small yellow eggs on a branch.
Mass storage of small yellow eggs: Up to 500 eggs can be laid by a single female silkworm.
Freshly picked mulberry leaves with unripe mulberries.
Mulberry leaves - the favourite (and only) food for silkworm mothers
A bunch of mulberry leaves with little silkworms on them.
The little silkworms, shortly after hatching.
A pile of large, white, fully grown silkworms on mulberry leaves are the feast for the eyes.
After about four weeks the silkworms have grown considerably. Soon they will pupate.
From small branches a rack was built, at which the caterpillars can pupate themselves.
Construction of frames on which the caterpillars can pupate.
A silkworm next to an already pupated silkworm moth on a mulberry leaf.
The silkworms begin to pupate.
Silk spinner pupal in different stages: a caterpillar with thin silk threads around it and a completely closed cocoon.
Gradually a completely closed cocoon develops.
A pupa without cocoon kept in a hand.
A pupa without a cocoon.
A transformed silk moth in front of his silk cocoon
Freshly hatched. One of the first silkworm moths sees daylight again.
A freshly hatched silkworm on its silk cocoon.
Welcome back! The giant silkworm has become a small butterfly.
  

After hatching, the little caterpillars are very hungry. They are fed fresh mulberry leaves several times a day so that they can grow and pupate after about a month. Fortunately, there are still four mulberry trees on the grounds of the Francke Foundations. Because the hungry caterpillars devour vast quantities. Thanks to regular feeding and uniform climatic conditions, the caterpillars grow rapidly. After four to five weeks, the silkworms are big enough. They begin to spin their silk thread and pupate in their cocoon. The children have built racks for this purpose to help the caterpillars pupate on.

The cocoon consists of a single silk thread up to 900 metres long. The construction of the cocoon takes about 3 to 4 days. After that, the caterpillar transforms into a moth. Some of the silkworms have not managed to build a cocoon. In the wild they would probably be too obvious prey for predators. However, in the shelter of our plant garden they have started the pupation process. The school garden children could watch the caterpillar contracting more and more and changing colour.

The children had to be patient for three weeks before they could marvel at the miracle of metamorphosis: the first moths dare to come out into the daylight and hatch from their cocoons. They fight their way out through a tiny hole in the cocoon, which they have created with a corrosive intestinal fluid. Once the head has made it through the hole, everything happens very quickly and the silkmoth is back as a moth. Immediately after hatching, the moths still seem quite dazed. They do not fly at all. They wait for their conspecifics to start mating. It takes several hours for the silkmoths to mate. Can you tell the females from the males? The children in the school garden have their own theory: "The females are fatter," they conclude. This seems logical, especially when the females are about to lay eggs. Between 400 and 500 eggs are laid by a single female silkmoth.

Shortly after laying the eggs, the moths die. The eggs can be stored for the next mulberry season, which begins in the planting garden as soon as the trees sprout fresh leaves again.

The history of silk production in Prussia

At the beginning of the 18th century, the art of silk cultivation, which originated in China, came to Prussia with the Huguenots. The cultivation of silkworms was soon regarded as a magic formula to combat the Prussian foreign trade deficit and to balance the national budget. The Prussian king therefore ordered that mulberry trees be planted all over the country to raise myriads of hungry caterpillars, from whose cocoons valuable silk threads were then to be extracted. On 17 February 1744, Frederick II (1712-1786) also ordered the Halle orphanage to establish a mulberry plantation for silkworm breeding »for the establishment and proper cultivation of which the orphans' children are to be used and constantly guided [...]«. Under the director Gotthilf August Francke (1696-1769), a nursery with over 4,600 larger and 15,000 young mulberry trees was established over the next two years on the site of today's high-rise buildings in Voßstraße. For the silkworms can only be fed with their leaves. The archives contain many records on this topical subject of the 18th century, including drawings and historical specialist literature. Three years later, the production of raw silk began here. In 1805, silk production had to be stopped due to adverse climatic conditions throughout Prussia. Silkworms are sensitive and actually at home in warmer regions.

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