The Acanthacorydalis fruhstorferi looks very similar to the dragonfly, but has huge teeth on the front of its head and looks very ferocious. The teeth of the males can be more than 3 cm long. Acanthacorydalis is a very small group of insects, belonging to the family Corydalidae of the in the order Megaloptera. At present, there are 8 known species in the genus, among which 6 are native to China. The largest aquatic insect in the history of the Earth, Meganeura, has a wingspan of 75 centimeters, but was extinct as early as 250 million years ago in the Permian period. In the past decades, the largest aquatic insect known is the helicopter damselfly endemic to Brazil and other places in Central and South America, with a maximum wingspan of 19.10 cm. In July 2014, the Acanthacorydalis fruhstorferi specimens collected by the Insect Museum of West China in Qingcheng Mountain of Sichuan Province have a maximum wingspan of 21.5 cm, which is nearly 2.4 cm wider than the helicopter damselfly. The specimen thus obtained the Guinness World Records Certificate in 2016. Despite its fierce appearance, the adults of Acanthacorydalis fruhstorferi do not prey on other animals, but only on sap from trees. The larvae live in clear streams or pollution-free rivers in mountainous areas, and catch small organisms in the water for food. Because of its high demand on water quality, its existence directly reflects the quality of local water, therefore regarded as a "water quality index" by many foreign experts.