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The odonates ( Odonata ), or odonatoptères , are one of Insecte S with lengthened body, equipped with two pairs of generally transparent membranous wings, and of which the made up and generally bulky eyes enable them to drive out their preys effectively. These are Prédateur S, that one can occasionally meet in any type of natural environment, but which is more frequently found with the accesses of the fresh water zones to brackish, stagnant with slightly current.

In French language, the term of dragonfly is in general employed in the broad sense to indicate the odonates, which gather both S of the young ladies (Zygoptera) and of the dragonflies sensu stricto (Anisoptera).

Morphology and anatomy

Like the other insects, the body of the odonates is composed of three parts: the head, the thorax and the abdomen, each one being formed of several segments.

The head carries the antennas (very short compared to other insects like the butterflies), the eyes made up of very many facets, three ocelles or simple eyes, and the oral parts of crushing type.

Behind of the head the thorax is. Classically composed of three segments as at all the insects, here the second and third segments with knowing the mésothorax and the métathorax are amalgamated and give the synthorax. The first segment, the prothorax, is very short, and carries the first pair of leg. The dorsal part of the prothorax, called the pronotum, often presents diagnostic coloured reasons allowing différencer close species, in particular for the females of certain species of zygoptères. The synthorax carries as for him the second and third pairs of legs, as well as the two pairs of wings.

The abdomen consists of ten segments. It can be of variable, more or less cylindrical or flattened, thickened or narrowed form to certain segments, and very often presents coloured reasons making it possible to identify the species of odonates. The tenth segment, rather short, carries anal appendices making it possible the male to seize the female behind the head during the coupling. It is also by observing the abdomen which one can distiguer the male and female individuals. The males carry the parts copulatrices under the second abdominal segment. In the females, the body allowing the fecundation and the laying of eggs, called ovipositor, is located under the eighth and ninth segments.

Morphological differences between zygoptères and anisoptères

The two sub-orders of odonates correspond to description made above but present some morphological differences making it possible to distinguish them:
  • eyes: large and joints at least in point at all anisoptères (except Gomphidae which has the separate eyes), the eyes are smaller and always separate at the zygoptères,
  • the wings: folded up above the body in
, home position (at the zygoptères), or extended to horizontal (at the anisoptères)

Reproduction and development

Become sexual ripe, the males will put themselves in search of a female to fertilize. The behavior varies from a species to another: research can be active, the male traversing its territory then, or passive, the male being satisfied to place itself in obviousness on a point of its territory while waiting for that a female passes in the vicinity.

The Copulation begin with the formation from the heart copulatoire: the male seizes the female behind the nape of the neck, between the head and the prothorax, thanks to its anal appendices. The couple forms a tandem then. Once posed on the vegetation, the female bends its abdomen to bring its bodies copulateurs (located under segments 8 and 9, at the end of the abdomen) in contact with those of its partner (at which these bodies are located at the beginning of the abdomen, under the second segment). The heart copulatoire is then formed ( cf photo on the right of a couple of Pyrrhosoma nymphula ). The male carries out then the exchange of the Spermatozoïde S.

The Fécondation at the odonates is indirect, i.e. that the spermatozoa will not fertilize immediately the female but are stored by this one.

Although they can very move away sometimes far from all Wetland, the odonates remain related to the aquatic environment for their Reproduction. The laying is always carried out in or near water, the female depositing its eggs either directly in water, or in alive or dead vegetable fabrics, whether they are watery or overhanging a water zone. According to the species, the behavior of the male varies at the time of the laying. At certain species, the tandem is maintained at the time of the laying. For others (in particular the species of the kind Calopteryx , the male remains near the female, and supervises the laying, in order to make sure that no other male comes to fertilize its female and does not replace its own spermatozoa. The males of other species are finally satisfied to break the tandem and move away from the female and do not take part in the laying.

The eggs, once hatched, give a pro Larve who then will begin his growth in water. After several successive moults, being able to be spread out over one more or less long period according to the species (of a few weeks to a few years), the larva climbs on a vegetable support out of water to carry out its last moult, known as moults imaginale, whose the adult will emerge finishes or Imago.

During emergence, the insect can only move very with difficulty, its body and its wings still soft must dry some time before being able to allow the vol. During this period, the adult in becoming is very vulnerable to all its Prédateur S.

Classification

Among the odonates one finds two sub-orders:

Anisoptère S (or Dragonfly S in a strict sense)

They are characterized by wings extended flat, nonpetiolate and unequal (former the narrowest than the posterior ones), often contiguous eyes, a fast flight, especially digger squat larvae, without gills (rectal respiratory room).

One distinguishes at the anisoptères, according to the classification based on the wing nervation complexes, the S following:

  • Family of the Gomphidae

    • Gomphus
    • Onychogomphus

  • Family of the Cordulegasteridae

    • Cordulegaster

  • Family of the Libellulidae

    • Crocothemis
    • Leucorrhina
    • Libellula

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