Workers with the Insect Museum of West China, who were recently given several very large dragon-fly looking insects, with long teeth, by locals in a part of Sichuan, have declared it, a giant dobsonfly the largest known aquatic insect in the world alive today. The find displaces the previous record holder, the South American helicopter damselfly, by just two centimeters.
The dobsonfly is common (there are over 220 species of them) in China, India, Africa, South America and some other parts of Asia, but until now, no specimens as large as those recently found in China have been known. The largest specimens in the found group had a wingspan of 21 centimeters, making it large enough to cover the entire face of a human adult. Locals don't have to worry too much about injury from the insects, however, as officials from the museum report that larger males' mandibles are so huge in proportion to their bodies that they are relatively weak—incapable of piercing human skin. They can kick up a stink, however, as they are able to spray an offensive odor when threatened.
Also, despite the fact that they look an awful lot like dragonflies, they are more closely related to fishflies. The long mandibles, though scary looking to humans, are actually used for mating—males use them to show off for females, and to hold them still during copulation. Interestingly, while their large wings (commonly twice their body length) make for great flying, they only make use of them for about a week—the rest of their time alive as adults is spent hiding under rocks or moving around on or under the water. That means that they are rarely seen as adults, which for most people is probably a good thing as the giants found in China would probably present a frightening sight. They are much better known during their long larval stage when they are used as bait by fishermen.
Via Dr. Stefan Gruenwald