Dragonfly larvae call the eggs of hydra (also known as water beggars) a special type when they hatch. Six feet and head are crowded together with the body, as inactive as a shrimp without feet. This stage is called "pre-juvenile stage". This stage is as short as three or five seconds, and as long as two or three minutes, the back of the pre-larva will crack, and the first larva will shed its skin and slowly open its mouth and move freely with its six feet. Different kinds of dragonfly larvae have different ages. Generally speaking, the younger the dragonfly larvae are, the lighter their body color will be, ranging from 8 ~ 16 years old. How does Hydra move in the water? Hydra breathes oxygen in the water by the rectal gills of the abdomen, so it breathes by slowly absorbing water and draining water from the tail end. Usually, except for six feet for crawling, in an emergency, the water inhaled in the abdomen will be sprayed backwards, and the generated force will drive them to move forward quickly to avoid enemies or prey. Usually, in order to avoid natural enemies and prey, hydra will be very close to the environment and form a protective color. Dragonfly larvae living in streams, such as damselflies, mainly feed on Diptera larvae, such as Mayfly larvae, stonefly larvae, Chironomid larvae and some small fish, while dragonfly larvae living in still water mainly feed on Diptera larvae, such as tadpoles, shrimps, small fish, Daphnia, smaller Odonata larvae, backstroke piles, dragonflies and Chironomid larvae. The natural enemies of young insects are birds, large omnivorous fish, safflower, negative larvae, lice and so on.

Biological characteristics: A dragonfly spends 95% of its life in water, and its larva is called Hydra. Because the visceral wall can't breathe in the water, his breathing frequency in the water has also accelerated a lot. So he can only shed his skin and hair. Water strips usually choose a sunny, quiet and sunny night, and under the cover of the night, they begin to change magically. If you emerge during the day, you will be attacked by carnivores. During the day, the temperature is high and your wings dry too fast, just like cicadas. Once in a state of hunger strike, Hydra always puts his abdomen up, that is, he puts his abdomen close to the water and draws oxygen from the air. Because they can't breathe in water with their gills as before, they can only breathe at the junction of water and air. When their underwater breathing system is shut down, they won't.

Hydra can catch prey even in complete darkness, and they can feel the change of water wave pressure with their tentacles and long legs, thus judging the size, orientation, shape and quality of prey. Dragonfly adults can eat all smaller insects flying in the air. Hydra is never picky about the food in the water. Once hungry, all aquatic creatures passing by him will become its food. When dragonfly eggs hatch, they are easy to become food for passing fish because of their fragile endoskeleton. When he surfaced, his instinct would urge him to leave the water he had lived for a long time-this was determined by a hormone in his body.