Last Updated on : Sunday, 09 October, 2016 01:23:05 PM


The compound eyes of dragonflies

Dragonflies and damselflies have large compound eyes that can see in all directions. When the compound eye is magnified several hundred times, each individual facet (ommatidium) is shown to be hexagonal in shape.

More on comparing the size, colour, and shape of the eyes of dragonflies...

A B C D E
Eyes separated widely from other Eyes meet partially along a seam Eyes barely touch at a centre point Eyes meet along a long seam Eyes close but not quite touching
Family Gomphidae Some of Libellulidae
Swam
Some of Libellulidae

Dragonflies active under strong sunshine

Family Aeshnidae
Some of Libellulidae

Dragonflies active at night.

 




Eyes of a male Nannophya pygmaea
Eyes of a female Lyriothemis cleis
Eyes of a male Brachydiplax chalybea
Eyes of  a female Agrionoptera insignis


Eyes of a female Camacinia gigantea

 

Tholymis tillarga (Fabricius, 1798)

 

WINGS
of dragonflies and damselflies

Adult Odonata (dragonflies and damselflies) possess two pairs  of  long, narrow, and net-veined wings. The wing veins of Odonata are fused at their bases and the wings cannot be folded over the body at rest.

 WINGS of dragonflies
Dragonflies
蜻蜓
WINGS of  damselflies
Damselflies
豆娘
Sub equal front and hind wings are not similar Both wings are equal and similar in size and shape
Dragonflies hold the wings horizontally outward when at rest.

Dragonflies hold the wings horizontally outward when at rest.

Damselflies hold the wings folded parallel with the abdomen or tilted upward

Damselflies hold the wings folded parallel with the abdomen or tilted upward

Family Aeshnidae
Gynacantha basiguttata
♀ 66mm

Family Gomphidae
Ictinogomphus decoratus
♂ 65mm

 Orthetrum pruinosum
♂ 44mm
 

Family Aeshnidae
Anax panybeus
♂ 92mm

Family Gomphidae
Sieboldius japponicus
♂ 83mm

Family Libellulidae
Agrionoptera insignis
♀ 43mm

Pseudagrion Pilidorsum ♂

Libellago Semiopaca ♀

Vestalis Amaryllis ♂

Family Calopterygidae
Vestalis amoena
♀ 50mm

Family Euphaeidae
Euphaea subcostalis
♂ 37mm

LibellagoSemiopaca_136

Family Chlorocyphidae
Libellago semiopaca
♀ 22mm

Family Coenagrionidae
Xiphiagrion cyanomelas
♀ 26mm


Frons of Dragonfly

 

 


In the dragonfly Tramea virginia, the secondary copularoty apparatus (SCA) on the venter of the second and third abdominal segments consists of

 1) the anterior and posterior laminae,

2) a pair of gential lobes and hamules,

3) the ligula,

4) genital fossa,

5) supporting frame work,

6) and the four segmented, highly specialized penis.

 

The penis head represnts the distal or fourth segment of the penis and bears paired lateral and apical lobes and a medial process.

The medial process includes

1) a sperm reservior,

2) a short sperm tube,

3) and paired cornua and inner lobes.


Dragonfly Parts

 


Like all insects, the dragonfly is made up of three main body parts: head, thorax and abdomen. The head is a tough, rounded capsule, hollowed out at the back to allow efficient attachment of the neck and to increase head mobility. The mouth is a complex hodgepodge of structures that you would not want to encounter in a dark alley. The upper lip, or labrum, is often considered part of the face. The lower lip, the labium (sometimes called the chin), is made up of three lobes. The labrum and labium function together to capture and secure prey while the jaws do the chewing. The jaws, which work from side to side, are made up of one pair of upper mandibles and two pairs of lower maxillae. These jaws, a series of incurved meat hooks, are worth a close inspection and should be approached with caution in larger species. A Dragonhunter and a large darner have both drawn blood from the thin skin between my fingers as I removed the beasts from my net. I hold no grudges; I suppose I had it coming.

The face is a conglomeration of plates separated by seams called sutures. The sutures are often darkened into stripes. The upper half of the face is the frons, and the upper surface of the frons is a shelf-like protuberance on which various diagnostic markings may be found. The compound eye is composed of nearly 30,000 lenses, which work in consort to provide a rich visual image to the dragonfly. They are sight-based creatures who, with a quick turn of the head, are able to scan 360 degrees as well as above and below. Their vision probably allows them to discern individual wing beats, which to us would appear as a blur. They can see ultraviolet and polarized light. Many species also see well in dim light.

Their two short bristly antennae are thought to function as windsocks or anemometers, measuring wind direction and speed, thereby giving them a method with which to assess their flight. By the way, dragonflies have no sense of hearing, cannot smell and are unable to vocalize.

The thorax is the center for locomotion. It is a muscular powerhouse, controlling head, wing and leg movements. Dragonflies are unusual in their wing movements. Most insects’ wings are attached to plates of the chitonous exoskeleton that are, in turn, attached to muscles that move the plates that move the wings. Dragonfly wings, on the other hand, are directly connected to large muscles within the thorax. The interior of the thoracic exoskeleton is massively braced and strengthened to withstand the pressures of these large flight muscles. This bracing can be seen through the exoskeletons of lightly-pigmented individuals such as the Wandering Glider, the Four-spotted Skimmer and the Common Green Darner.

Thoracic stripes are present in many species. In order to easily communicate the positions of these stripes, the thorax can be separated into three sections: top, shoulder and sides. The top stripes of the thorax will be found in the region between the head and the wings and are best viewed from the front of the dragonfly. The side stripes of the thorax are found below the hindwing attachment point and back toward the abdomen. The shoulder stripes are found below the forewing attachment point, in between the top stripes and the side stripes.

Legs are used for perching and for capturing prey. Many species have spines on the legs that form a type of basket in which prey is caught.

The anatomy of wings and their venation can be very complicated, and one could make a life’s work of just studying them. Most dragonflies can be identified to the level of genus and many to the level of species by just knowing the wing venation. The veins in the wings of dragonflies start as flattened tubes in the compact, tightly folded wings hidden inside the skin of the aquatic nymph. During transformation to adulthood, the veins fill with hemolymph, or insect blood, causing the wings to unfurl. Most of the hemolymph is drawn back into the body after the wings have been fully expanded. The empty tubes and the membranes dry, leaving crisp, tough wings.

The most obvious feature of a clear, unpatterned wing is the stigma, located on the leading edge of each wing out towards the wingtips. It is thought that the stigma may be used for signaling mates or rivals and may also act as a tiny weight that dampens wing vibrations. The nodus, located at the shallow notch midway down the leading edge of each wing, is an intersection of several large veins and is a point of both strength and flexibility. Because of the structure of the venation around the nodus, the wing is allowed to bend downward (during an upward stroke of the wing) but not upward (during a downward stroke of the wing), resulting in a powerful flight stroke without losing much energy on the return stroke. The wing triangles are located about twenty percent of the way from the wing base toward the tip. The relative size and orientation of these triangles on a dragonfly’s wings can be a clue as to the dragonfly’s family. Originating from an inner, rear corner of the hindwing triangle, the anal loop reaches down into the expanded base of the hindwing. The degree to which the anal loop is present varies from one family to the next.

The abdomen always has ten segments. Segments 1 and 2 appear to be integrated into the thorax and are sometimes difficult to tell from the thorax. To find a particular segment, it is usually best to start with segment 10, far out at the tip, and count backwards. Because of its segmented nature, the abdomen is very flexible and is able to arch up or down (but not side to side). Learn to count abdomen segments as many of our descriptions are based on them.

The male testes are located in segment 9. Due to the unique nature of dragonfly copulation, the male must transfer sperm to his secondary genitalia, called the hamulus, located in the underside of the second and third segments. The hamulus is a complicated set of “surgical tools” that the male uses for removing the reproductive “investment” made by other males during previous matings. Other parts of the hamulus are then used by the male to fertilize the female with his own sperm. The terminal abdominal appendages of the male are called claspers. The claspers are formed by a pair of upper appendages, called cerci, and a single lower appendage, an epiproct. In some species, the males possess auricles on the sides of segment 2 whose function is to help direct the female’s genitalia to a proper fit with the male’s secondary genitalia during copulation.



The female terminal appendages consist of a pair of cerci, which have little or no function. In some species, namely the Shadow Darner, they are very brittle and tend to break off. Underneath segment 8 there is either an ovipositor or a subgenital plate, depending upon the species. Both structures are for laying eggs and extend over segment 9 and possibly beyond.




 


 

INDEX OF DRAGONFLY

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