What is Odonata?
Three suborders in Odonata.

Odonata constitutes a widely distributed order of insects. The some 5500 species belong to three suborders: the Anisoptera (dragonfly), the Zygoptera (damselfly) and the Anisozygoptera. In Japan, there are 217 species and subspecies belonging to these three suborders. The Anisoptera, which is called 'TOMBO (except Aeshnidae)' or 'YAMMA (Aeshnidae)' in Japanese, has such features as follows: the shape of fore wing being different from that of hind wing; typically large and active; robust body and wings; and wings opening while perching. The Zygoptera, which is called 'ITO-TOMBO (except Calopterygidae)' or 'KAWA-TOMBO (Calopterygidae)' in Japanese, has such features as follows: four similar shaped wings; small and inactive; slim body and wings; and wings usually closing while perching.

an anisopteran and a zygopteran
Left : Macromia amphigena amphigena belonging to Suborder Anisoptera;
Right : Mnais costalis belinging to Suborder Zygoptera.

The Anisozygoptera contains only one species in Japan, called 'MUKASHI-TOMBO' in Japanese, which is one of the most well-known insects all over the world, although it is one of relatively common species in Japan.

an anisozygopteran
MUKASHI-TOMBO, Epiophlebia superstes Left : An adult laying eggs, Right : A F-1 larva.
Copulation and Oviposition

Males usually wait for females near the water. There are many species which form a territory at this time. When a male finds a female, he rushes for her to grasp her and to form tandem which is so-called 'O-TSUNAGARI' in Japanese. They copulate after forming tandem and then the female begins to oviposit being guarded by the male.

Wating for female
Left : A male Sinogomphus flavolimbatus wating for females with perching.
Right : A male Sinogomphus flavolimbatus grasping a female coming to lay eggs.
Tandem and copulation
Left : Tandem formation of Sympetrum gracile,called 'O-TSUNAGARI' in Japanese.
Right : Copulation of Paracercion calamorum calamorum with perching.

Odonates generally lay eggs in the plant tissue in, or above, the water (endophytic), or directly onto the water (exophytic). All Zygopterans, which have 'a perfect ovipositor', lay eggs in the plant tissue. Females of Aeshnidae (Anisoptera), which also have a perfect ovipositor, lay eggs in various substrate, such as live plant tissue, dead plants or mud.

Varius ovipisition
Left : A pair of Sympetrum darwinianum laying eggs above the grass onto the mud (arrow: an egg).
Right : A female Polycanthagyna melanictera laying eggs into rather dry mud near water.
Egg development

Eggs hatch in a period of from some 10 days to more than 100 days after being laid. The duration of egg stage shorter than ca. 40 days is called 'direct egg development', i.e. eggs which hatch promptly without diapause, and that longer than ca. 80 days is called 'delayed egg development', i.e. those which hatch only after a prolonged period greatly exceeding that needed normal morphological development.

The latter is adapted to survive the inclement period such as winter or drought season. In Japan, Sympetrum, Lestes and Aeshna fall into the latter type. They generally lay eggs in autumn; overwinter in egg stage; and hatch during from spring to early summer. The former, on the other hand, includes dragonflies which breed in spring or summer and generally overwinter in larval stage.

Larval development

 Larvae are generally aquatic. They moult 9 to 14 times until emergence. Duration of larval stage is various: the shortest one is about 30 days and the longest one about 6-8 years.

Larvae
Left : A larva of Aeshna juncea juncea which has swelling wing sheath.
Right : A full grown larva of Planaeschna milnei just before emergence breathing in the air.

There are various morphological types in this stage, which are as the result that adaptive radiation has taken place. It is said that the morphological and ethological adaptations shown by larvae to their environment are associated with one of three processes, i.e. respiration, feeding and concealment. For example, there are two types of respiratory organs, 'rectal gills' and 'caudal gills'. The Anisoptera and Anisozygoptera have the former type, and the Zygoptera has the latter.

Larvae
Left : An anisopteran larva, Somatochlora uchidai, without caudal gills.
Right : A zygopteran larva, Copera annulata, with three caudal gills.

Dragonflies do not have a pupal stage.

Emergence

There are two types of emergence, i.e. upright type and hanging type. Calopterygidae, Coenagrionidae, Platyenemididae, Lestidae, Petaluridae and Gomphidae fall into the former, and Epiophlebiidae, Cordulegastridae, Aeshnidae, Corduliidae and Libellulidae into the latter.

Two types of emergence
Left : Hanging type emergence: Epitheca marginata.
Right : Upright type emergence: Trigomphus interruptus.
Adult stage

After emergence, adults move from their emergence site. The distance of the movement is various among species. An extreme example is the case of a cosmopolitan species, Pantala flavescens, which crosses the ocean from south to Japan. Another longer example is the case of Sympetrum frequens, or 'AKI-AKANE' in Japanese, which migrates to high land about more than 100 km far from the emergence site. Adults return to, or seek for, the water when they are mature.

Immature imagos
Left : A cosmopolitan species Pantala flavescens migrating over the Ocean.
Right : A Japanese endemic Sympetrum frequens migrating to high land from the plain pond it emerged.

 Adults are active and good at flying. Most of dragonflies belonging to the Anisoptera and Anisozygoptera usually fly by counterstroking, that is, the beat cycle of fore- and hindwings are shifted by a half-cycle, so that whenever one pair of wings move down, the other is moving up (see the figure below). The flight of dragonflies is, thus, extremely rapid and straight. In many of Zygoptera and Anisoptera with colored wings such as Rhyothemis, all four wings sometimes beat in synchrony.

Death
Left : A robber fly feeds a dragonfly Sympetrum eroticum eroticum.
Right : Sympetrum risi risi.
Feeding

Odonates are carnivorous through their life without exception. They feed on small animals, such as Chironomus or Tubifex, in the larval stage, and, in the adult stage, on flying insects, sometimes relatively large ones such as cicadas. Their large eyes are convenient for catching their foods on the wing. Dragonflies such as Aeshna tend to go after moving materials in the air. 'BURI', or 'TORIKO', is a Japanese traditional method of catching dragonflies which utilizes the tendency.