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.
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.