Late May and Early June is the season for mulberries in the United States. Mulberry trees thrive in warm temperate and subtropical regions of Asia, Africa, Europe, and the Americas. Mulberries are widely distributed because the berries are a favorite food of the birds who scatter the seeds in their droppings.
A mulberry tree is not very distinctive, but if it is close to a sidewalk, the sidewalk will be covered with berries that fall from the tree. The immature berries are white or light green, and they turn red and then dark purple as they ripen. The berries can be harvested individually from the low-hanging branches, but it is easier to put a sheet under a branch of a tree and then shake the branch. Some of the berries will bruise and the sheet will be stained with purple spots, but this is the best way to gather enough berries to make a pie or some preserves. Wine can also be made from the berries. Mulberries are rich in anthocyanins which are colorful pigments with beneficial health effects that may include the prevention of cancer.
There are many varieties of mulberry trees. Silkworms will only eat the leaves of the white mulberry tree (Morus alba). Silk production, or sericulture, has been practiced in China for at least 5,000 years. Domesticated silkworms are entirely dependent on humans and no longer occur naturally in the wild. Domesticated silkworm moths cannot fly. They have been bred selectively for improving the quality of the cocoon and silk production.
Silk moths lay their eggs on the mulberry leaves, and the worms hatch after fourteen days. The worms feed on the leaves continuously, and they molt as they grow. After molting four times, the larvae enclose themselves in a cocoon of raw silk produced by their salivary glands. Silk is basically a protein consisting of the amino acids glycine (60%), alanine (20%), and serine (20%). Inside the cocoon, a silkworm transforms into a pupa that emerges as a moth in about three weeks. The moths reproduce and die within five days, but in this time the female manages to lay from 200 to 500 eggs to continue the life cycle.
Silk is harvested by dipping cocoons in boiling water to kill the pupa and help unravel the thread. Each cocoon contains a single silk thread that is about 300 to 900 meters long. Silk from China was known to the ancient Greeks and Romans. The silk road toward the west was opened by the Chinese in the 2nd century AD. Large caravans carried huge quantities of beautiful textiles to the coasts of the Mediterranean. Although silk has been displaced from many applications by synthetic fabrics, more than 80,000 metric tons of silk are produced yearly, principally by China and India.