White Mulberry

Morus abla L.

by John Brouwer

Extending over the fence behind block one and onto the sidewalk is a white mulberry tree which is now covered in fruit. Mulberries are made into jellies, jams, pies and added to baked goods. Mulberries also make a good wine. As far as I can tell, most of our mulberries are left on the tree and no one, except the birds, is taking advantage of its bounty.

Over thousands of years, the mulberry tree has a history completely intertwined with human economies.

The white mulberry is the foundation for the silk industry started in China around 2700 BC. Over the centuries silk became a precious commodity and China carefully guarded its secrets. In 139 BC, the world's longest highway was opened, stretching from China to the Mediterranean. It became known as the silk road. The demand for silk was so great within the Roman empire that emperors hired smugglers and some were successful in bringing mulberry seeds and insect eggs into the Mediterranean. These became the foundation of the French and English silk industries, which thrived through the 18th and 19th centuries.

Silk is produced by the larvae of the moth, Bombyx mori, which is probably the most domesticated of all insects. The silkworm feeds exclusively on white mulberry leaves. Thousands of eggs and worms are kept on special racks and, during the time between hatching and spinning their cocoons, the worms have to be fed fresh leaves every few hours. If conditions are kept right, the worms eventually spin cocoons made up of a strand of silk several thousand feet long. The silk is a fibroin protein secreted from two silivary glands in the head of each larvae. This thread is unraveled, treated, and woven into silk cloth. Around five thousand silkworms consuming 250 kg. of mulberry leaves are needed to produce one kg. of silk.

Our white mulberry was introduced into eastern United States during the colonial period to set up a silk industry. Efforts were largely unsuccessful. In the 1830's the US government extensively promoted silk worm production and thousands of people planted white mulberry trees. The efforts to produce silk were a bust but tens of thousands of white mulberry trees were introduced into eastern North America, where they became invasive.

The civil war made southern cotton unavailable in the north. An American naturalist in Boston, Professor L. Trouvelot, brought the eggs of the gypsy moth over from France in order to cross breed them with the silkworm moth with the hope of producing a more resilient silkworm for a northern textile industry. A few caterpillars escaped from his home, found a very hospitable environment, and became the gypsy moth plague that causes $100's of million in damages to North America's forests each year.

In the meantime, the white mulberry naturally interbred with the native red mulberry to produce a new hybrid. This interbreeding is leading to the extinction of the native red mulberry, as the red mulberry pollen can't compete with white mulberry pollen.

This hybridization has become so extensive that there are only some 80 red mulberry trees left in Canada. Red mulberries are still found in a few sites in southern Ontario; Hamilton's Royal Botanical Gardens, Ball's Falls Conservation Area, Niagara Glen, Rondeau Park, Point Pelee Park, Pelee Island, Middle Island, and East Sister Island. Red mulberry is now considered the most endangered tree species in Canada. Researchers at the University of Guelph are developing a red mulberry recovery plan.

The extinction of the local red mulberry, illustrates the danger of introducing genetically modified organisms into the environment. GMOs can easily hybridize with indigenous species and we will lose the genetics which have protected the plant and humans for tens of thousands of years.

All the above is related to the tree overhanging our fence. Maybe some enterprising Beaver Creekers would consider getting some Bombyx mori. By setting up sericulture in their basements, Beaver Creek could become the last stop on the old silk road.

July 2008