Last Updated on : Sunday, 09 October, 2016 10:03:02 PM
The abdomen of odonates
ABDOMEN DIFFERENT BETWEEN MALE AND FEMALE DRAGONFLIES
Most male dragonfly abdomen is often narrower at segment 3, whereas the female abdomen is more robust.
1- Male abdomen is often narrower at segment
| For the female dragonflies , genitalia are located underneath the abdomen between segment 8
Zygoptera and some Anisoptera (Aeshnidae and Cordulegaster) have an ovipositor, surrounded by valvae.
An ovipositor is used to stick eggs in plants, wood or mud. These species are called endofytic.
Species that don’t have an ovipositor (exofytic) simply drop their eggs into the water.
At the back of segment 10, at the tip of the abdomen, the appendages are located. These are especially clearly visible at male odonates.
Anisoptera males only have upper appendages, plus one single small knob that is
also called lower appendage.
The abdomen is divided into 10 segments, numbered from 1 at the base to 10 at the tip. The major features of the abdomen useful for identification are the sexual appendages, extending from the terminal segments, and the secondary genitalia of males. The latter are located under abdominal segment 2. Of the many intricate structures that make up the secondary genitalia, the most useful to learn for field identification are the hamules, which are hook like structures on most dragonflies; they are visible with a hand lens and are often species specific in shape. The terminal appendages of males, which are used to grasp females by the rear of the head (in typical dragonflies) or the thorax (in damselflies) during mating, are often important features for distinguishing look-alike species. It is therefore worthwhile to learn the names and positions of these structures. The cerci (singular, cercus) are the pair of upper (superior or dorsal) appendages. When the male curls his abdomen down and forward to grasp the female, the cerci curl under the upper rim of the head (in typical dragonflies) or contact the mesostigmal plates (in damselflies).
Male cerci are often relatively large
appendages with hooks or spines for grasping. The cerci of females
are typically simple, cone-shaped or leaﬂike structures and only
occasionally of use in field identification.
Some species of damselﬂies have a vulvar spine on the rear lower margin of segment 8 that projects over the genital opening at the base of segment 9. You will occasionally ﬁnd odonates, especially damselﬂies, with tiny red “beads” attached, often in small clusters, to the undersurface of the thorax or abdomen. These are not part of the odonate but rather are larvae of parasitic water mites, which hitch a ride on odonate larvae and then make the transfer to the adult form at the time of emergence. The mite larvae attach themselves to the hardening body, sucking ﬂuids from their host. When the adult odonate later comes into contact with water— for example, during oviposition—the mites detach and return to the water to complete their life cycle.
are few other insects that might be mistaken for odonates. Perhaps
most likely to cause confusion are adults of the antlion family (Myrmeleontidae,
order Neuroptera), which resemble adult damselﬂies but have
noticeably longer, clubtipped antennae.
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).
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.
The abdomen of odonates, which consists of 10 segments
plus the rudiment of an 11th segment, is remarkably long and slim, rarely very
broad and short. The abdomen houses the internal organs and the genitalia. It
also acts as a steer and helps keeping balance in flight.
Segment 1 is very short and not visible from above. Segment 3 to 7 are quite long, the others are shorter. Segment 10 carries a few projections called anal appendages.
Each segment consists of an upper side or tergite and a bottom side or sternite, connected by pleurites at the flanks. The tergites are much bigger and harder than the sternites, which are quite weak and flexible.
The genitalia of odonates are very complex. Males have their sperm production organ in the 9th segment (like any other insect) but their copulation organ (that acts as a penis) is located underneath segment 2. These organs are not interconnected, so the male has to transfer his sperm from the producing organ to the penis before the actual copulation takes place!
The penis (called ligula) is an important characteristic for the recognition of male Zygoptera in case of doubt.
The hamulus - A pair of hooks in segment 2
For libellulidae (a group of Anisoptera), the hamulus can be used for species recognition. The hamulus is a set of hooks situated at the sternite of segment 2, used to hold the female’s genitalia during copulation.
Prior to the selection of a willing female, the male will transfer sperm from his testes located on the underside of abdominal segment 9 to his hamulus located on the underside of segments 2 and 3. This is accomplished by simply arching the abdomen until the undersides of the appropriate segments make contact.
Mating is normally initiated by the male who,
with the grace of a professional wrestler, uses his legs to grasp the female by
her head and thorax. Curving his abdomen forward, he uses his two cerci and the
lower epiproct as a clamp and clasps the female by the back of the head. They
are now “in tandem.” Mating is accomplished by the male arching his abdomen
downward while the female arches her abdomen toward the male’s hamulus. Once
connected, the pair is in the wheel position or “in copula.” Still connected,
the pair will usually fly up to the safety of treetops to mate, although some
species do copulate in mid flight. The male commences a purging of the female’s
genital opening. He uses the hamulus to remove, squash or push out of the way
any sperm that the female may still be carrying from prior matings with other
males. This process ensures his genetic investment in the clutch of eggs that
the female will soon lay. The time needed to complete fertilization ranges from
15 seconds to well over an hour.
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 like a set of “surgical tools” that a male uses for removing sperm left 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.