Trichoptera insects (commonly known as caddis) are the sisters groups of moths and butterflies. The marriage and flight behavior of stone moths is an important strategy for their survival and reproduction. How did this behavior evolve over billions of years of time and space on Earth? Why was the dominant Trichoptera before the Cenozoic era overtaken by its sisters Lepidoptera These issues, which have attracted much attention from the paleontological community, have recently been unveiled by Chinese scholars through in-depth research on hundreds of amber specimens of insect aggregation behavior: as early as the mid Cretaceous period, stone moths had already engaged in mating flight behavior, and as a precursor feature of the Theropoda order, their mating flight behavior was also influenced by the pressure of newly evolved predators during the same period. This important research on the "past and present" of Trichoptera was completed by the scientific research colleagues of Capital Normal University, the Institute of Zoology of the Chinese Academy of Sciences, Hebei University of Geosciences, the National Museum of Nature and the University of Kansas in the United States. The achievement paper was recently published in the National Science Review, a comprehensive academic journal of natural science, under the title of "Wedding and Flying Stone Moths in the Middle Cretaceous Period". Professor Ren Dong, the corresponding author of the paper and a professor at Capital Normal University, introduced that swarming behavior is a phenomenon where insects actively gather together, and mayflies, stone moths, stone flies, and dipteran insects have the habit of swarming. When insects fly together, groups of male insects produce pheromones or sounds to attract distant females, greatly increasing the chances of insects finding mates to mate. He pointed out that many ancient insect groups have been able to undergo billions of years of environmental changes, and their reproduction to this day is due to their unique survival strategies. Similarly, many insects in the order Trichoptera exhibit mating flight behavior. In this study, Dr. Wang Jiajia from Capital Normal University, the first author of the paper, discovered through examining hundreds of amber specimens of insect aggregation behavior that the mouthparts of the stone moth were extremely degraded, the penis was elongated, the female abdomen was significantly enlarged during male and female mating, the compound eyes of the male were larger, the wing shape was wide, the wing wear of the insect body was different, and there were significant differences in the number of males and females. Subsequently, the research team further counted and measured various morphological parameters of the specimens. Based on the typical sexual dimorphism of insects that flew during marriage, principal component analysis and other methods ultimately confirmed that these Cretaceous stone moths gathered together due to marriage. A total of 5 extinct species have been found in these married and flying stone moth specimens, including the branch Lymantria litura under the family Lymantidae, the Queqiao Gushi under the family Lymantidae, the Qixi Gushi, the Gathered Gushi and the Hydrangea Gushi. Ren Dong said, "Nature has frozen the most beautiful love in the world in its way, so we have given these new species names full of love.". On this basis, the research team further explored the evolutionary history of marriage flight in the order Trichoptera. Through full evidence phylogenetic analysis, they constructed an evolutionary tree of Trichoptera based on a dataset of 16 families and 75 species (including extant and fossil species), and conducted ancestor state analysis on the existence of marriage flight in various groups of Trichoptera. The results showed that marital flight behavior is a common derivative of the order Trichoptera, and it may have been present since the first appearance of the order; In the subsequent evolutionary history, marital flight behavior was only lost in a few species of the suborder Trichoptera, family Trichoptera, and family Trichoptera, while in the suborder Trichoptera, marital flight behavior was missing in multiple lineages, including family Trichoptera, family Trichoptera, family Trichoptera, family Trichoptera, and family Trichoptera. The author of the paper and visiting professor at Capital Normal University, Shi Zonggang, believes that although marriage flight can greatly increase the efficiency of reproduction, it also increases the chance of being preyed on because a large number of insect individuals gather together, which is a natural "feast" for predatory insects. Zhang Weiting, the author of the paper and associate researcher at Hebei University of Geosciences, said that since the Mesozoic era, the main threat faced by flying insects has been an increasing number of flying predators. During the Paleozoic era, the main flying predators were only dragonflies, and the earliest pterosaurs appeared during the Triassic period. Dr. Qiu Rui, the author of the paper and the National Museum of Nature, stated that based on the structure of teeth and skull, many basal pterosaurs from the Triassic to Middle Jurassic mainly fed on insects. Starting from the Late Jurassic, newborn birds became the main flying predators of insects. In the early Cenozoic era, bats appeared and quickly radiated globally. Skull fossils showed that the basal bat, the Ishin bat, had the ability to locate echoes, indicating that they were mainly active at night, while tooth fossils showed that they mainly fed on insects. The author of the paper, Professor Michael Engel from the University of Kansas in the United States, believes that in order to avoid being detected by bat echolocation, many insect groups have evolved features that can detect ultrasound after the Eocene, such as the tympanic earbuds of the Noctinoptera, Tettidae, and Crickidae families. However, this feature is lacking in both living and fossil specimens of the Trichoptera order, which means that Trichoptera insects do not have the ability to detect bat ultrasound. Research has shown that the marriage flying stone moth is one of the favorite foods for bats, as the signals generated by a large number of insects gathering are more easily detected by ultrasound than individual insects. Ren Dong pointed out that although birds, pterosaurs, and dragonflies caused significant predation pressure on flying insects during the Mesozoic era, ancestral state analysis results showed that only a very small number of evolutionary branches of the order Trichoptera experienced the disappearance of mating flight behavior during the Mesozoic era. This is because the vast majority of pterosaurs, birds, and dragonflies were diurnal animals, and the mating flight of stone moths mainly occurred at dusk and night. However, in the new generation, the situation became more severe due to the emergence of nocturnal flying predator bats. The research team concluded that the presence of bats may have exerted strong predatory pressure on the mating flight behavior of the order Trichoptera, and many branches of the order lost their mating flight behavior in the early Eocene, which is likely a response to bat predation. As a sisters group of Trichoptera, thanks to the emergence of angiosperms, Lepidoptera has achieved a perfect encounter with flowers, and large-scale radiation occurred in the Cenozoic, rapidly surpassing Trichoptera to become the second largest order of insects. (Lai Xin She)