If you don’t understand, just ask, why are there silkworm pupae hanging on ginkgo trees?

Before reading the article, a reminder

The pictures in this article may trigger insect fear

People often ask on social platforms, why are there silkworm pupae hanging on roadside trees?

Cocoons hanging on the ginkgo tree | Xiaohongshu user @爱打油的柿子

Save money: This is the pupa of Zhou's gnawing wasp, used to control the American white moth.

In 2003, the National Environmental Protection Agency and the Chinese Academy of Sciences released "China's First List of Invasive Alien Species", which included seven species of animals. Among them, the only one that can cause large-scale environmental damage, great psychological impact and visual pollution to people is the gypsy moth.

A white moth lying on a tree trunk | TampAGS / wiki commons

"Autumn Caterpillars" spread wildfires

Hyphantria cunea, a member of the family Hyphantria, is commonly known as the Fall webworm . It is a world-famous quarantine pest and an international forest plant quarantine target.

White moth larvae | Katja Schulz / wiki commons

Unlike the Australian cockroach and the German cockroach, the American white moth is native to North America. It spread to Europe across the ocean with military supplies during World War II. It was first discovered in Hungary in 1940 and spread like wildfire to most parts of Europe except Northern Europe in the following decades.

In 1945, the gypsy moth landed in Tokyo, Japan, along with military supplies, arriving in Asia for the first time. It later reached South Korea during the Korean War and moved northwards into North Korea. In 1979, the gypsy moth appeared in Dandong, Liaoning, and officially invaded China. Today, the gypsy moth has spread to more than 30 countries in the North and is also found in New Zealand.

Main distribution areas of the gypsy moth today | gd.eppo.int

The gypsy moth is an inconspicuous moth. It is the most common small white moth in the family Lysimachia. It has a hairy head and thorax, which looks very cute. The coxa and femur of the forelegs are yellow. The wings of female adults are white, while males usually have black spots. The larvae are grayish yellow with dense grayish-white long hairs. The hairs are not toxic, but may cause allergies if they come into contact with the skin. The larvae have red heads and black heads. The red heads are only found in North America.

Left: a pure white male adult of the white moth, a female laying eggs, an adult with spots, a red-headed larva, and a black-headed larva. | Andrei Sourakov / Florida Museum of Natural History

Invasive species with full attributes

The gypsy moth has all the characteristics of an invasive species. First of all, it is not picky about food . The gypsy moth's diet is very diverse, ranking first in the entire class of insects. Its hosts include almost all broad-leaved trees and shrubs, flowers, crops, weeds, and even gymnosperms that you can see or not see. There are 120 species of plants in the United States, more than 300 species in Japan, 234 species in Europe, and 94 species in Dandong, China alone. There are 636 species of gypsy moth hosts recorded worldwide .

During each major outbreak, the first target of the gypsy moth is generally broad-leaved trees used as greening along the roadsides, or broad-leaved trees and fruit trees in the countryside , such as sycamore, mulberry, sugar maple, poplar, willow, ash, apple, cherry, etc. After eating all the leaves of one tree, they will collectively migrate to another tree. After eating all the broad-leaved trees, they will start eating crops and wild plants.

Maple tree eaten by gypsy moth larvae | Andrew C / wiki commons

The American white moth is highly adaptable. It can tolerate low temperatures and overwinter in the northeast; it can tolerate high temperatures and survive at 40 degrees; it can tolerate hunger and the fifth-instar larvae can go without food for ten days or half a month and will not starve to death even when transported long distances with timber and other trade activities.

In addition to artificial spread, the adult gypsy moth has a strong ability to fly . The first batch of gypsy moths that invaded China in 1979 were adults that flew from Sinuiju on the other side of the Yalu River. When migrating to find food, the larvae can crawl 500 meters, and can also ride the wind and waves and spread by water . Because there are many host plants, every time the gypsy moth arrives at a new location, it can establish a colony, reproduce, and even change its diet to adapt to the local plants.

White moth building a web in a willow tree | Alison Hunter / wiki commons

The invasion lasted only a short time, but the potential harm was huge

The gypsy moth has been in China for less than 40 years and has caused damage in 11 provinces and cities in Northeast, North, East and Central China, with the furthest reaching Shanghai. According to climate forecasts, 55% of China's land is suitable for the gypsy moth , and the potential damage in the future is huge.

Scientists predict the potential distribution areas of the American white moth. Red indicates very suitable distribution areas. | Xuezhen Ge /

Projecting the current and future potential global distribution of Hyphantria cunea (Lepidoptera: Arctiidae) using CLIMEX

In most parts of China, the gypsy moth has three generations a year, with the second generation from August to October causing the most serious damage. When an epidemic breaks out, it is all over the place. The larvae of the gypsy moth before the fifth instar will weave a dragnet between the branches , where they feed day and night. After eating, they will move to another place to weave a net to feed again. The larvae of the 6th to 7th instar will not weave a net, but feed in a dispersed manner. The mature larvae will crawl down the tree to a suitable place to pupate. Wherever they go, "the boundless fallen leaves rustle down, and the endless swarms of insects roll in." All the street trees have been eaten up. When the larvae migrate, they will fall on people's heads and bodies like raindrops, and they will also crawl into residents' homes in groups, and even occupy beds, seriously invading residents' privacy. In Hebei Province, Liaoning Province, Shandong Province and other places where the epidemic is serious, residents are often scared and dare not go home.

White moth builds a web in a persimmon tree | Lyle J. Buss / University of Florida

The "silkworm pupae" hanging on the tree are its natural enemies

At present, there are many methods to deal with the gypsy moth, such as artificial physical control, chemical and biological control, parasitic natural enemy control, and sex pheromone trapping . The gypsy moth has not been in China for long and has not yet evolved a particularly strong resistance to pesticides . The combined use of various biochemical agents such as avermectin, diflubenzuron, and Bacillus thuringiensis has a good effect. The technical application of the parasitic natural enemy Chouioia cunea, which is specifically targeted at the gypsy moth, is very mature and is widely used in areas where the gypsy moth occurs.

The process of Zhou's parasitoid wasp parasitizing the American white moth | Bei Xin /

Research and application of Chouioia cunea Yang (Hymenoptera: Eulophidae) in China

Although there are reliable means of controlling the gypsy moth, it is too tenacious, and due to the uncertainty and uncontrollability of its spread, as well as the impact of climate, it often rebounds 2 to 3 years after being eradicated. If it is not managed in time, it will still cause serious consequences. Although it will eventually be eradicated, the damage has already been done, so it is very important to establish a complete quarantine monitoring system. The gypsy moth has spread to the world due to war and commercial trade, and has risen around the world. This is the price that human civilization has to pay for its gradual development, but I hope this is an affordable price.

Author: Frost Moth

Editor: 媗媗、Calendar Girl