Insects exist alongside us in almost every corner of the planet. According to data from February 2019, there are 927,965 insect species recorded in the Catalogue of Life (CoL), the most comprehensive catalog of species in the world.
The Museum houses many large insects that are seen as the kings of the insect world, behemoths in this microcosm; some are even Guinness World Record holders. Their size is beyond our comprehension.
Before introducing them, let's take a look at some ancient giant insects.
This giant mayfly larva on the fossil originates from Inner Mongolia and dates back to 165 million years ago. Its body is more than three times the size of the largest mayfly larva in modern times. And going back to about 300 million years ago, the wings of a dragonfly could be as long as 72 centimeters!
Ancient insects were so large because the oxygen content in the atmosphere was as high as 35%, whereas now, the oxygen content in the air is only 21%.
Insects do not have lungs and only absorb oxygen through tiny tracheae located all over their bodies. The high concentration of oxygen in the air provided the basic elements of life for many giant organisms. The activity of insects requires high metabolism, and a higher oxygen concentration means more effective cellular respiration, so high oxygen levels make insects evolve with larger body sizes.
Another reason for their size was the less number of predators that ancients insects had in comparison to their modern counterparts.
Take the ancient dragonfly. Back then there were no pterosaurs (flying reptiles), birds, or bats in the air, making them the apex predators of the sky. Free from the threat of becoming prey, they grew larger and larger.
But the rule of giant insects in the sky ended after the emergence of birds. The increased mobility of predatory birds then became the driving evolutionary force for flying insects. A smaller size gave them more flexibility and increased their ability to hide, and were more conducive to avoiding prey of birds.
The gradual decrease in oxygen concentration led to an increase in the number of predatory flying animals such as birds and bats, and therefore a gradual decrease in the size of insects. As a result, few large insects exist now.
However, some giant insects still survive in tropical rain forests with relatively high oxygen concentrations where they can conceal themselves easily, such as the Amazon rainforests of South America, the rainforests of Southeast Asia, the island of Madagascar, and the tropical rainforests of central China. Recent investigations have also led to the discovery of some giant insects in the south of China.
On June 1, 2016, the Insect Museum of West China received a beautiful certificate from the Guinness World Records that said, “The largest aquatic insect (pterygota) is a dobsonfly (Acanthacorydalis fruhstorferi), which has a wingspan of 21.6 centimeters and was discovered in Chengdu, Sichuan, China on 23 July 2015. The specimen is on display in the Insect Museum of West China.”
This was the first time a Chinese insect became a record holder in the Guinness World Records.
In the past, the largest aquatic insect in the modern world was recognized as the helicopter damselfly from Brazil. Its maximum wingspan was only 19.10 centimeters and the length from its head to the end of its abdomen was 12 centimeters, which is 2 centimeters shorter than a male Acanthacorydalis fruhstorferi.
The largest aquatic insects that have existed in Earth's history was Meganeura. Although their wingspans could reach 72 centimeters, they became extinct as early as the Permian Period 250 million years ago.
The Acanthacorydalis is a small genus found only in mainland China, the Assam area of India, and northern Vietnam. Currently, there are 8 species in the genus, 6 of which are found in China.
Their larvae live in clear streams or unpolluted mountain rivers, hiding between rocks and catching small aquatic creatures. They prey on a variety of aquatic insects, including tadpoles and small fish. Adults are active at night and have strong phototaxis, so they can be seen occasionally near waterside lamps. It is a representative species of Corydalidae family.
Adults have transparent, broad, cicada-like wings. Both males and females have giant teeth at the front of their heads. Its teeth can grow up to nearly 3 centimeters in males, hence their name in Chinese means the 'giant-tooth dobsonfly'. Although the pairs of giant teeth look ferocious, these insects do not prey on other animals, but rather feed on tree sap. Their only objective after eclosion is to mate. Their eggs are normally deposited between stones near flowing water.
In nature, insects in the Corydalidae family are very sensitive to water quality. Females choose to lay their eggs in clean water, and the larvae will continue to live in water after being hatched. When there is water pollution or sudden changes in pH, the larvae cannot adapt to it and will disappear quickly from this area. Therefore, their existence is a direct reflection of the quality of local bodies of water and they are used by many foreign experts as 'living water quality indicators.'
Regrettably, however, the distribution of these 'living water quality indicators' has greatly declined in the past 30 years and they have all but disappeared in many parts of the world. Take the area surrounding the city of Panzhihua in Sichuan Province. The Acanthacorydalis orientalis that used to live here were regarded as a local delicacy called 'sand worms' or 'Anning fameflower'. Hundreds of thousands of these insects were captured each year, resulting in the species' near disappearance from the area in recent years.
Some scientists have conducted an experiment in which a small amount (approximately 0.5 milliliters) of dilute hydrochloric acid was added to a cubic meter of clean water. As soon as the hydrochloric acid was added, the Corydalidae larvae became unresponsive and their movements became clumsy. When the amount of hydrochloric acid was increased to 0.8 milliliters, the larvae stopped eating and eventually died. This experiment explained why the dobsonflies were disappearing from areas surrounding cities: urban pollutants mix with rainwater and change its pH, which pollutes the waters around cities. Dobsonflies disappear from these areas because they simply cannot adapt to these changes.
Many places in China are feeling the effects of human activity and urbanization, and more and more pollutants are being released into the rain.The current habitat of the Acanthacorydalis fruhstorferi is shrinking, their distribution is gradually becoming more isolated to mountain areas where the water is free from pollution. Corydalidae have not been observed in the wild in many of Sichuan's mountainous regions for several years. The Museum's specimen of the Acanthacorydalis orientalis (with wingspan of 16.8 centimeters) was collected 26 years ago from the Weijiang River on Mount Qingcheng.
In the past, many people would think that the Acanthacorydalis are not involved in our daily life and their existence is meaningless to us. However, as a part of Earth's closely interconnected ecosystem, the abnormal disappearance of each species will have a butterfly effect on the entire system and will eventually affect our own lives. As a species that shares the Earth with us, the current state of the dobsonflies sounds a warning bell for the deterioration of our own living environment and as such, has attracted mankind's attention. Just as the US magazine Newsweek joked, if bugs with the size of personal pizzas become a regular fixture of their daily lives, instead of becoming terrified, villagers of Chengdu (it seems the US media is under the impression that Chengdu must be a mountain village since it is home to such bizarre insects) "will find comfort in the cleanliness of their water."