How long do dragonflies generally live, and are they beneficial insects or pests?

Dragonflies are the collective name for insects of the families Libellulidae and Aeshnidae in the order Odonata, belonging to the hemimetabolous insects, with about 5000 species worldwide, about 300 species distributed in China, among which there are many kinds of the most common dragonflies, such as Anax parthenope, Pantala flavescens and Ischnura senegalensis, etc. So how long do dragonflies generally live? Are dragonflies beneficial insects or pests?

I. How long can dragonflies live

The dragonfly larva, the nymph, must spend at least one year in the water. The time required for the entire larval stage varies according to different species and seasons, ranging from one month to three or four years, and those that take longer must endure seven or eight years before they can emerge as adults. The lifespan of the adult dragonfly is only one tenth that of the larva, living only about 1-8 months. Even so, dragonflies still count as long-lived among insects.

II. Are dragonflies beneficial insects or pests

Dragonflies are beneficial insects. The nymphs in the water can prey on mosquito larvae or other small animals, and sometimes they even cannibalize their own kind. Both adults and larvae are carnivorous, mostly eating pests. Besides being able to prey on large numbers of mosquitoes and flies, adults can also prey on pests such as butterflies, moths and bees, so they are truly beneficial insects. The appetite of dragonflies is also very astonishing. A kind of large green dragonfly commonly known as “Qingtouleng” can carelessly eat about 2000 aphids and other such small flying insects in a day. It is said that a single Anax parthenope can eat nearly 1000 small flying insects in a day, and can eat 40 flies or 840 mosquitoes in 1 hour. At the same time, dragonfly larvae are especially fond of eating mosquito larvae, and one dragonfly larva can eat more than 3000 mosquito larvae in a year.

III. Where do dragonflies go in winter

Dragonflies have basically completed their entire life cycle before winter, but dragonfly eggs will be placed inside plants, inside dead wood or even in dry soil, or else dropped on the water surface, depending on the species. The eggs of most temperate-region dragonfly species will not hatch after being laid, and may wait several months before hatching into nymphs. This non-hatching period is called the “diapause period”, and its purpose is to allow dragonflies to pass through the cold winter in the form of eggs.

IV. What food do dragonfly larvae eat

The diet of dragonfly larvae is related to species. Usually, dragonfly larvae inhabiting streams mainly feed on mayfly nymphs, stonefly nymphs, chironomids and other dipteran larvae as well as some small fish, while species inhabiting still waters mainly feed on tadpoles, small shrimps, small fish, water fleas, smaller dragonfly nymphs, backswimmers, mosquito larvae, chironomids and other dipteran larvae. The larval stage is the longest period in a dragonfly's life. The first stage or instar of the nymph after the dragonfly hatches is called the pronymph, which has no legs and usually lasts only a few seconds to a few minutes. After this first molt, the nymph enters the second instar, with simply constructed legs and three segmented antennae. Dragonfly nymphs have different numbers of instars depending on the species, ranging from 8 to 16 instars. The time required for the entire nymph stage varies according to different species and seasons, ranging from one month to three or four years.

The above is the Tuliu website editor's related introduction to the habits of dragonflies. The process of dragonflies emerging into adults is very long, and they can eliminate a great many pests, making them truly beneficial insects.