Morphology & Anatomy

Morphology and Anatomy

Juveniles

Nymphs are the juvenile stages of insects. Dragonfly Nymphs (Naiads) are aquatic, and acquire oxygen through gills. They are voracious feeders, and eat aquatic insects. Some large Nymphs can eat small fishes, tadpoles too.

Head is narrower than thorax, and body is stout in Dragonfly nymphs.
Dragonfly nymphs have internal gills, they pump water inside the body and gaseous exchange occurs through the gills present in abdominal cavity.

Head is wider than thorax, and body is slender in Damselfly larvae.
These nymphs have external gills through which they acquire oxygen.

Adults

Dragonfly Morphology

Front and hind wings dissimilar in size and shape, the hind wing considerably wider at the base than the fore wing.
Eyes meet mid-dorsaly, and separated by a space less than their own width.
At rest, wings are held horizontally. They are strong flyers.

Damselfly Morphology

Front and hind wings similar in size and shape.
Eyes separated by more than their own width.
At rest, wings meeting above the body or only partly expanded.
Generally with weak, fluttery flight.


Eyes: Dragonfly and damselfly adults and juvenile both have large eyes, and they depend on their eyesight for finding ad catching prey.
Both dragonflies and Damselflies have compound eyes, as in all the insects. Each compound eye of Odonates is made up of around 28000 individual units (omnaetidia) which almost cover the head , and more than 80% of brain is devoted to analysing visual information.

Wings: Wings are membranous structure, made up of chitin. They are very thin, (2-3 micrometer) and have extensive venous network for strength and flexibility.
Following picture shows major parts which constitute a wing of an Odonate.


Pterostigma: (pteros+stigma in greek means wing+marking ) It is a dark pigmented spot on the leading adge of a wing. It is present towards the wing tip and stands out due to coloration. Experiments have shown that pterostigma, being heavier than surrounding areas of the wing, helps insect for gliding by reducing the vibrations within the wing.
Veins: Veins are hollow tube like structures which carry Haemolymph (nutritious fluid, like blood), which nourishes wing and prevent it from being brittle. Positioning of veins is very critical because they control structure of a wing during flight and affect flight efficiency.
cross venation (veins connecting longitudinal veins) is found in Odonate wing, which is very primtive characteristic, and is lost in many other insects.

Some Important Terms

Labium - Extendible mouth part underneath the head by which prey is captures.
Mandible- Jaw ( food is crushed by mandible )
Femur, Tibia and tarsus - parts of leg.
Thorax -
Gills- Respiratory structure in aquatic animals, where water is pumped in for gaseous exchange ( dissolved oxygen from water is taken )
Abdomen -