The terror of the insect world?

One reason might be that they are carnivorous predators and eat many smaller insects. The adults fly around and catch smaller insects in the air, while the larvae hunt smaller insects and other invertebrates under water. Also, many dragonflies are very large for insects. However they are completely harmless to humans and do not bite, sting or carry disease. In fact, they are good for humans because they eat harmful insects such as mosquitoes.