The Hine's Emerald Gallery Page 1

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Dragonfly Anatomy        What is a juvenile?        Female and male juveniles

How do adult females and males differ?        The thorax       The abdominal segments

What are the legs for?        Do dragonflies age?

 

The graphic at the right shows a male Hine's Emerald with the wings and legs removed for the sake of clarity. The general morphology of the dragonfly is shown. The first thoracic stripe is yellow in the juvenile state, then becomes cream-colored, and with age it often becomes white in appearance.

Juveniles

A juvenile S. hineana doesn't have emerald eyes

Shortly after the last larval stage leaves the water and crawls onto a stalk of sedge or other vegetation, or a rock if vegetation is not available, the young adult emerges. The larval exoskeleton left behind is called the exuviae, and the newly-emerged dragonfly (called the teneral stage) inflates its wings until they are outstretched, and quietly waits until its wings and exoskeleton are dry. During this time, the young dragonfly is highly vulnerable to predators, such as birds and frogs. Once the wings and exoskeleton are dry, the juvenile vibrates (called "whirring") its wings a few times and takes to the air to become the beautiful flying predator it was meant to be. With time, perhaps a week or so, the juvenile exoskeleton continues to become sclerotized (hardened) and pigmented (colored) as the dragonfly begins feeding away from the water from which it escaped. Shown below are two juvenile females.

The Hine's Emerald female shown in Fig. A was photographed June 6, 1999. It was the first Emerald seen that spring. Field studies indicate that most of the earliest juveniles seen along trails and open areas are females. Males are seen somewhat later, and by then most have already acquired their adult coloration. Other studies involving capture and release suggest that males and females may tend to patrol different areas during young adulthood (Soluk, Foster et al, Illinois Natural History Survey). In juveniles and young adults, the eyes are reddish or greenish and lack the emerald luster of older adults. The thoracic stripes are yellow instead of gold or cream color (see arrow in Fig. A), and wings have a broadly amber tint that becomes localized near the wing bases with age.

Shown at the left is another juvenile female where the red coloration of the eyes is clearly seen. The eyes will acquire their emerald green coloration and the yellow stripes along the thorax will fade to a gold or cream-color as the juvenile female ages. Note the red coloration on the "shoulder" of the thorax. The deep red coloration of the eyes in this juvenile is unusual. It may be that sunlight was oriented such that eye pigments strongly reflected wavelengths in the red part of the visible spectrum.

Two views of the anterior end of the same juvenile female are shown below. The reddish color on the anterior thoracic "shoulder" plate is clearly seen in the lateral (A) and dorsal (B) views of the female, and with age the plate becomes a reddish brown.

As indicated above, in June when  Hine's Emerald dragonflies are first seen along the trails of The Ridges Sanctuary there are mainly females. Infrequently, males are seen, and the one shown below is one of the few photographs of a juvenile male taken to date. The image was recorded June 18, 1999.

This male has eyes characteristic of the juvenile state, along with yellow thoracic stripes. The anterior, dorsal thoracic plate is not fully pigmented. Note the typical profile of the abdomen of the Hine's Emerald male, with its narrow "waist" and an expanded posterior portion. The tripartite structure of the clasper is well-shown (the role of the clasper in the mating process will be discussed in the next section in some detail).

Adults

On a sunny day, before mating begins, juvenile and adult Hine's Emerald dragonflies spend most of their time airborne feeding on other flying insects. When adulthood is attained, dragonflies devote their lives to both food and sex, the effect of which is to ensure survival of their species. Since, on sunny days, they spend most of their time aloft, significant photo opportunities arise only when they perch briefly, perhaps to rest or devour an oversize meal. Obviously, studying or photographing dragonflies requires a great deal of patience, and no small amount of luck.

At the lower right are dorsal views of two adult Hine's Emerald dragonflies (Fig. A is a female, Fig. B a male). The body color is typical, appearing dark brown or green, often depending on lighting conditions.  Flecks of yellow may be seen along the lateral aspect of the abdomen. Wingspan of S. hineana is about 3.3 inches while body length ranges from 2.25 to 2.5 inches.                                                               

Figure A shows the characteristic profile of the female's abdomen, which is relatively straight for most of its length. The abdomen of the female is several millimeters longer than that of the male, which is shown in Fig. B, even when the length of the female's paired extensions at the posterior end of the abdomen are disregarded. The dragonflies in Figs. A and B are in scale with respect to one another, so size comparisons can be made directly between the two images.

In Fig. B, the tapered "waist" of the abdomen is evident. The tip of the abdomen is enlarged in the inset, and the two dorsal elements of the clasper are apparent. As in all dragonflies, the abdomen consists of 10 segments (see image below), and some dragonfly specialists believe that an 11th segment became modified into the clasper in the male and the posterior abdominal extensions of the female. These extensions, as well as the two dorsal elements of the clasper complex, are designated cerci (singular: cercus).

An adult female Hine's Emerald is shown below; the dragonfly was photographed hanging vertically from a twig, but the image has been rotated to show the body in a horizontal position. The main anatomical features are clearly shown. The stripe on the second thoracic segment (called the mesothorax) appears white while the stripe on the most posterior thoracic segment (the metathorax) is still yellowish. These are the wing-bearing segments of the thorax and they are fused together to form a box-like structure. The prothorax, the most anterior of the three segments, is small. All three segments bear paired legs that appear to be designed for perching, and, when the dragonfly is in flight, for grasping prey.

                                  

Note that there are 10 abdominal segments, with #1 and #10 being small. The abdominal segment in the Hine's Emerald usually has a large, roughly triangular, spot on each side. The spot is yellowish or cream-colored. Note what appears to be a stiffening (or reinforcing) plate on the underside of abdominal segment #3. This occurs only in the female. The profiles of the ovipositor/cerci complex in this specimen is typical for the female Hine's Emerald.

Side views of female and male Hine's Emerald dragonflies are shown below in typical "resting" or "roosting" poses, whereby they hang vertically or at a slight angle from a small twig. The angle is almost always less than 40 degrees from the vertical. Dr. Tim Cashatt, a dragonfly specialist with the Illinois State Museum, feels that the legs of S. hineana, and many other large dragonflies, cannot easily support the body weight in a horizontal perching position. Thus, when at rest, these dragonflies literally "hang around." The legs appear to provide for perching and feeding. In the latter case the legs are thrust forward as the dragonfly approaches its prey to form a somewhat funnel-shaped "food basket." Stiff hairs on the legs help to snare the insect's next meal. Most often, the dragonfly approaches prey from underneath.

Figure A shows a lateral (side) view of an adult female with the abdomen appearing as a straight-sided cylinder. The abdominal cerci are shown by the arrow, and just above and to the left the spout of the ovipositor can be seen. The shape of the cerci and ovipositor vary among different species of dragonflies.

Figure B is a typical adult male, with its thoracic stripes appearing white instead of yellow or cream-colored. This suggests that this is an older male. Although the anterior waist-like narrowing of the abdomen is seen, the more posterior part is not as expanded as in younger males. This suggests that the testes of this old male (which are located in the expanded part) may be less active, or that this male has already transferred sperm to the female. The arrow in Fig. B indicates the lower member of the clasper, called the epiproct. The epiproct and the dorsal two cerci can open and close against each other, creating a vise-like structure that plays a key role in copulation, as will be discussed later.

Do dragonflies age? Of course. With age their wings become ragged looking, with small pieces or even large pieces (sometimes a whole wing) missing. Much damage to wings may occur when females lay eggs in and around aquatic vegetation. In both males and females, the shape of the abdomen may change following copulation and egg-laying. Flights in older dragonflies may be of shorter duration and wing beat more erratic. And they perch more often. Shown below at the left are dorsal views of two older females.

Figure A shows an older female with pieces missing from the wings (the arrow shows a missing piece). Note that the abdomen is slightly misshapen toward the posterior end, which could mean that this female completed her egg-laying, with depletion of the internal store of fertilized eggs. A feature of older females is that the posterior portion of the abdomen becomes grayish, as in Fig. B. Presumably this occurs as a consequence of egg-laying, where the ovipositor (and the end of the abdomen) is repeatedly thrust below the water surface as eggs are deposited, with the abdomen becoming discolored in the process. Another possibility is that some of this gray color is due to pruinescence. Pruinescence is due to the secretion of a whitish, powdery substance, onto the surface of dragonflies as they age (as in Libellula julia, the Chalk-Fronted Corporal). The posterior tip of the abdomen of the female in Fig. B is shown at greater enlargement in the inset, and the paired cerci are clearly seen. Although the abdomen of the female in Fig. A appears slightly collapsed, the abdomen of the female in Fig. B appears swollen toward its end (the significance of which is unknown).

 

 

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