Insects may not have developed brain， but that does not mean they will not have the sense of fear. A recent study on dragonflies by Canadian biologist found that dragonflies are very sensitive to the surrounding environment. When the predator appears in front of them， even if they are not in danger of being eaten， they will be scared to death because of the fear.
　　Researchers at the University of Toronto put a group of dragonfly larvae （dragonfly larvae are aquatic animals） and fish predators in the same aquarium and separated them with shelter materials. The dragonfly larvae can see the fish， and smell them， but the fish cannot eat those dragonfly larvae. As a result， the survival rate of dragonfly larvae who have seen the fish is only 19% to 29% of that of normal dragonfly larvae.
　　Dragonflies are chosen by researchers as the research objects because they are larger in size compared with other insects， besides they are extremely agile flying animals and among one of the fastest flying insects. Dragonflies are so agile flying animals， but still die under pressure from which we can see the harm of pressure. This study can be applied to all organisms facing any pressure and lay a theoretical foundation for future research of "lethal effects of stress".