Last Updated on : Saturday, 01 July, 2017 06:25:14 PM
| Family Libellulidae | FAMILY AESHNIDAE |
The largest dragonflies on the planet. Also the fastest flying dragonflies.
species in Borneo
Indaeschna Fraser, 1926
|Genus : Oligoaeschna Selys, 1889||
Gynacantha Rambur, 1842
Heliaeschna Selys, 1882
|Genus : Tetracanthagyna Selys, 1883||
|Genus : Linaeschna Martin, 1909||
|Genus : Anaciaeschna Selys, 1878||
Genus : Indaeschna
The genus comprises just two species, the other being restricted to the Philippines.
A spectacular and common dragonflies to be found inside the rainforest of Malaysia is Indaeschna grubaueri . It is another very large species (Male hw, 63-65 mm) quite the equal of any Tetracanthagyna except plagiata. In both the male and female the head and thorax are brightly marked with green and the abdomen has broad lime green bands at the distal end of segments 2-6 or 7. The wings are hyaline, sometimes smudged with brown in older specimens. By virtue of its striking colours and size it is unmistakable and is easily identified on the wing. It is most commonly seen in the day inside the forest where males hang in the shade beside suitable breeding sites—shallow bottomed leafy pools, small rocky pools formed in depressions in dry stream beds and even large rot holes and buttress pans (pools formed when tree buttresses grow to form a cavity which fills with water). The females are encountered when they arrive to mate and lay their eggs. Larvae are large and may live at very high density in close confinement. They appear to have lost the cannibalistic instincts found in other aeshnid larvae. Later instars feed voraciously on the tadpoles of many species of frog. Development in smaller bodies of water may take two to three years. The adults are semi-crepuscular, emerging into the open to feed in the late afternoon, sometimes coming to light. They occur from sea level up to about 800 m, mostly in hilly country in mixed dipterocarp forest.
|The Aeshnidae is a well defined group with over 400 species worldwide. In Borneo
29 species in 8 genera. These constitute an interesting mix of very widespread
endemic or regional ones.
The family includes medium-sized to enormous species (hw 35-80+ mm).
The female of Tetracanthagyna plagiata may have the greatest wingspan of any living anisopteran and it is reputedly the heaviest of all odonates.
Aeshnids are typically robust species with dark colours, often marked with green or less often blue or yellow. The eyes are very large and dark green.
The discoidal triangles of fore- and hindwings are similar in shape and orientation, a condition unique to this family. The wings are typically hyaline but are often suffused with a smokey brown coloration which darkens with age. A few species have opaque brown patches on the wings and sometimes there is a broad dark streak along the costa, or leading edge of both wings.
The abdomen is long and thin, sometimes extremely constricted at segment 3.
Male anal appendages are usually long and thin, and minute differences in their structure are often critical for species identification.
The Aeshnidae are the only anisopteran family in the region in which the female has an ovipositor and eggs are inserted into vegetation or debris.
A great many species are crepuscular or even partly nocturnal and almost all may be active until sunset. Some are eocrepuscular—that is they fly before sunrise.
It is quite common for aeshnids to come to the lights of buildings at night.
Aeshnids mainly breed in standing water, including forest pools, open ponds, drains and large phytotelmata. Tetracanthagyna larvae occur in streams. The larvae are elongate and the labial palp is armed with a strong movable hook. Many are fierce predators, taking large tadpoles and small fish. There is far less variation in their body form than in the Gomphidae, but the armature of the mask varies a good deal according to diet.
Genus : Oligoaeschna
Oligoaeschna species are medium to moderately large and rather heavily built.
In colour they range from dark reddish-brown to black, marked darkly with green.
They are among the smallest of the Bornean aeshnids. Apart from their distinctive form, they may generally be separated from most other members of the family by the presence of fewer crossveins in the discoidal triangle, which is usually divided into only three cells in both wings, uncommonly four, whereas in most other genera it is usually divided into five or more, and never fewer than four cells.
In most species the male wings are lightly and uniformly coloured, generally a pale amber, but females often have extensive semi-hyaline reddish-brown patches.
The male superior appendages are only moderately long and are robust, in many cases flattened and expanded.
Female appendages normally break off with mating, but when intact they are long and very broadly paddle-shaped with a thin stalk. The function of these long racquet like appendage curious structures is unknown.
Males are generally separated by the structure of their anal appendages although species also differ in their markings and wing venation.
Females show a good deal of interspecific variation in wing venation, wing marking and the shape of the abdomen.
Oligoaeschna is one of the more taxonomically difficult genera of the Anisoptera. Seven species, four endemic, are recorded from Borneo to which may be added a probable further four, known only from females, which were described but not named by Lieftinck in his 1968 revision and key (Tijdschrift voor Entomologie 111: 137-186). To this should be added that some specimens recently collected in Brunei do not fit well with any forms discussed by Lieftinck and may either represent undescribed females of known males or undescribed species.
0. buehri, is a distinctive species widespread in lowland swampy areas throughout Borneo and Sumatra.
O. buehri male anal appendages for the otherwise similar with 0. foliacea and 0. amata
0. venusta, (hw 44.5 mm) known from south-east Borneo is the largest species, this species are recognized by the presence of very dark patches at the base of each wing.
In females of other species the dark coloration may be either more extensive or lacking entirely. In several the abdomen is spindle-shaped—that is constricted at segment 3, expanded at 4-6, then constricted again.
Oligoaeschna species are not common in collections and it is unusual to see them in significant numbers. All species seem to have much the same habits. They are most frequently found in swampy country and alluvial forests in the lowlands. They are mainly found in forested areas but not necessarily primary forest. Both males and females are attracted to lights of houses at night and it is common in some situations to see mixed assemblages of two or three species hawking for small insects around the forest canopy. By aeshnid standards they are not rapid in flight, and they may hawk back and forth over an area of a few metres square if there is a suitable gap in the canopy.
Typically Oligoaeschna begin activity up to two hours before sunset and as dusk approaches are joined by later-flying Gynacantha, Heliaeschna and Tetracanthagyna. They are quite unmistakable silhouetted against the sky, in particular the females which hold their extraordinary spatulate appendages splayed almost at right angles to each other. Sometimes when they are flying beyond reach of a net it is possible to attract them lower by tossing small pieces of gravel ahead of their flight path, which they follow mistaking them for insects. Females are sometimes encountered in deep forest in the middle of the day. They are regularly active at this time, flying quite slowly, and are probably searching for oviposition sites. The larvae are not known, but in their habits they may be similar to Sarasaeschna pryeri, which was formerly included in Oligoaeschna. Larvae of this species live a semi terrestrial existence in swampy bogs. I once witnessed an Oligoaeschna female in Brunei ovipositing in a nearly dry, leaf-filled depression in degraded alluvial forest.
Linaeschna polli (Plate 12b) is the only species of a primitive genus thought to be related to Oligoaeschna. It was described in 1909 from a single male from Brunei Bay, and that remained the only known example until 1997 when a second male was taken in the Crocker Range (Kimanis Road). Nothing is known of its habits but it is apparently a lowland species and is almost certainly crepuscular, possibly nocturnal and perhaps sometimes comes to light. In appearance it has many features in common with Oligoaeschna evident in the wing venation and the slight spindle shape of the abdomen. The inferior appendage is bifurcated at its tip. However it is immediately distinguished from any known species of that genus by its larger size (c? hw, 53 mm) and by the characteristic broad, dark brown costal streak on all four wings reaching back as far as the triangle. Similar markings are present on Tetracanthagyna degorsi and T. plagiata males but both species are considerably larger (minimum male hindwing for degorsi is about 58 mm, plagiata is much larger). In Tetracanthagyna the pterostigma is short and the inferior appendage undivided. There are also considerable differences in venation.
Genus : Gynacantha
Gynacantha is a genus of mainly large species found throughout the world's tropics. Seven species are found in Borneo, one endemic. The males are generally recognized by the very swollen, almost spherical base to the abdomen with large rounded ear-like auricles on segment 2 followed by an extremely constricted third segment and long, thin, simple superior appendages. The base of the abdomen is often very colourful with bright green flecks on the dorsum and bright blue auricles, but some species are more sombrely coloured. The easiest way to separate both males and females from the sometimes similar Heliaeschna is by the lack of any crossveins in the median space at the base of the wing (see Fig. 28f & g for an illustration of this character).
Very similar to Gynacantha dohrni in size and structure are the endemic Gynacantha demeter, the widespread but uncommon Gynacantha subinterrupta and the slightly larger Gynacantha maclachlani from north and west Borneo. All differ from one another in slight details of the male appendages and the coloration of the thorax and are quite difficult to separate.
By far the largest Bornean species is the rare Gynacantha limbalis (S hw, 61 mm). The superior appendages are quite straight and narrow as in dohrni but the inferior is between one third and half the length of the superiors. Also there is a distinctive brown streak along the leading edge of both wings. It might be mistaken for a Tetracanthagyna species but for the basally swollen abdomen constricted at the third segment. In Borneo it has been recorded only from Sarawak.
A fairly common and ubiquitous species, and easily the smallest member of the genus (S hw, 37-41 mm), is Gynacantha bayadera (S appendages, Plate 14b). It is immediately
recognized by the basal segments of the abdomen which are only slightly swollen, the auricles which are triangular instead of semicircular, the less pronounced constriction of the third segment and the fairly short, absolutely straight superior appendages. The hindwing is relatively broad, being as wide as in the considerably larger Gynacantha dohrni.
Female Gynacantha are difficult to identify to species. They are typically a little larger in wingspan than the males and have extremely long, slightly spatulate anal appendages. These however are seldom intact and apparently always break off during mating. The third abdominal segment is distinctly constricted, though less so than in the males.
Gynacantha species are found from lowland swamp forest to about 1000 m in the case of basiguttata, bayadera and dohrni. Typically they are seen hawking at dawn or just before and after dusk and in these situations it is quite common to see virgin females with intact appendages which in flight appear very like males. In the evening they become active later than Oligoaeschna, and they often come to artificial light. During the day they may be found resting in deep undergrowth or in overhangs at the head of small gullies, but from noon onwards they may be reproductively active around shallow leaf-bottomed pools in deep forest shade. Males of basiguttata and dohrni guard these pools, or if the pool is large, several males may share it, each defending a well defined territory. They perch conspicuously on emergent twigs with the abdomen hanging vertically in the manner typical of all aeshnids. Females arriving are normally mated before they are allowed to oviposit, inserting their eggs into dead leaves and twigs. The larvae are typically aeshnid in general form, but are easily separated from other genera by the presence of long fine bristles on the labial palps. They are found in leafy forest pools but may be difficult to discover among deep layers of litter.
Another widespread genus in tropical Asia and Africa is Heliaeschna. Species are generally a little larger than Gynacantha and are easily distinguished from this and most other genera by the presence of at least one cross vein in the median space at the base of the wings (see Fig. 28f). They are dark green, or brown-black darkly marked with green. In the male the base of the abdomen is normally swollen, but not excessively so and the auricles are triangular and pointed backwards, not marked with blue as in many Gynacantha. In most species the third segment is constricted. The females are slightly larger, with the abdomen only slightly constricted if at all and the hindwing well rounded. They have long anal appendages as in Gynacantha but these are almost always broken off. Heliaeschna species are very crepuscular in habit, apparently never becoming active until after sunset and feeding and mating well into the night. Whether they are also active before dawn is uncertain. They may be common in peat swamp forest and swampy alluvial forest on the plains but are seldom recorded from the hills. Nothing is known of their life history, although it seems probable they breed in standing water. Five species are known from Borneo, most of which are probably quite common but are not often collected except when attracted to the lights of buildings.
The largest and commonest are H. idae and H. crassa (Plate 14f & g. Fig. 146) which fly together and are very similar except for the fine structure of their elongate thin appendages and the presence of a small
dark brown spot at the base of each wing in crassa. They are similar in size (c? hw, 49-54 mm) with idae perhaps a little larger. The females normally have dark brown smoky wings, sometimes with a distinct subapical band and are almost impossible to tell apart. H. simplicia (S appendages Plate 14 h, Fig. 147) is a smaller species (S hw, 45-46 mm) with pale elongate flattened male anal appendages and five crossveins in the median space at the base of the wings. The wings are only lightly tinted in both sexes. H. uninervulata is similar in size and general appearance but has only a single crossvein in the median space. Its male anal appendages are similar to those of simplicia, though a little broader. H. barteisi is also about the same size (d hw, 45-47 mm), but has 4-7 cross veins in the median space of its exceptionally narrow wings. The male abdomen is a very little constricted with the anal appendages straight sided and moderately broad. The genus was treated in a thoroughly confusing way by Martin in 1909 in the aeshnid volumes of the well known catalogue of the Selys collection, and it is important if using this work to consult later corrections.
Tetracanthagyna includes some of the largest dragonflies in the world. They are dull brown insects, sometimes with pale bands on the thorax. The male abdomen is scarcely swollen basally and never constricted; the female abdomen is thick, short and tapered with tiny appendages. The wings are frequently marked with brown along the costa and may have broad subapical bands in the female. The pterostigma is unusually small. There are four species in Borneo. All are thought to breed in forest streams and are active before dawn and after sunset. They occasionally come to the lights of houses and most specimens are captured in this manner. The best known is doubtless T. plagiata (Fig. 148) the female of which is said to be the largest species ofAnisoptera in the world in terms of both wingspan and weight ($ hw, 80-84 mm) (Plate 15a). It is difficult to appreciate the size of this enormous insect until it is held in the hand or set against other very large species which at once seem to be of only average size. In nature it often flies with a seemingly slow
flutter but usually high in the subcanopy and difficult to see in the fading twilight. Matti Hamalainen reports several times seeing the female at very close quarters laying eggs in a large fallen trunk above a stream in Pahang. The male is significantly smaller but is still huge (hw, 73-75 mm). Its wings are marked heavily with brown along the leading edge, a colour form also found in the female. It is extraordinarily swift on the wing and very hard to capture in the half light of dawn or dusk. Both sexes have two broad pale bands at the sides of the synthorax which, along with their size, easily distinguish them from species with similar wing markings. It occurs mainly in lowland alluvial forest but may forage higher along exposed ridges. T. degorsi (Plate 15b) (S hw, 63-65 mm, $ hw, 65-67 mm) is marked in both sexes with a brown costal streak along each wing, a little less extensive than in male plagiata, from which it differs mainly in the unbanded, uniform greenish-brown sides of the thorax. It is also a good deal smaller than plagiata but has similar habits and is very difficult to capture on the wing. It breeds in clear streams and at night the larva, rather small in relation to the adult, leaves the water and perches head down on emergent sticks, its eyes about the level of the water surface. Apparently from this position it captures surface swimming fish. T. degorsi is probably the commonest and most widespread member of the genus in Borneo and has been taken around 900 m at Poring Hot Springs. T. waterhousei is slightly smaller (<S hw, 57 mm, $ hw, 66 mm) and is distinguished by its almost unmarked wings and two broad pale bands on the side of the synthorax. Like plagiata it is found in lowland alluvial forest and swamp. Its larva is similar to that of degorsi in appearance and habits. It is the most widespread of the Tetracanthagyna species, ranging from Bengal and Hong Kong to Sundaland. T brunnea (9 hw, 67 mm) is known only from the female, which has a plain unbanded reddish-brown thorax and a broad subapical band on the wings. A similar colour form is said to occur in degorsi, with which it might be confused.
Anaciaeschna jaspidea is the single member of its genus found in Borneo. In general form and wing shape it is quite like a small Anax (see next page) but its body coloration is quite different, being mainly reddish-brown above with two striking broad yellow stripes on the synthorax. The basal segments of the abdomen also are pale bluish to yellow at the sides. The male hindwing ranges from 41-46 mm. It is a very widespread Indo- Australian species found in a variety of disturbed, shallow water habitats and the margins of natural lakes, from salty mangrove lagoons to marshy
drains up to 1200 m. It is active in the early morning before dawn and around dusk. In Sabah I have seen it flying over the beach at the seaside in late afternoon, but in general it does not seem to be very common in Borneo.
The cosmopolitan genus Anax is represented by two species, the Indo-Australian A. guttatus (Plate 14a, Figs. 151 & 152) and A. panybeus which is also widespread in Asia. Both species are large robust insects (S hw, 51-54 mm) with a heavy thorax and broad hindwings. In males as well as females the anal angle of the hindwing is rounded. Older specimens often develop quite a dark brown tint to the wings, concentrated especially near the base of the hindwing. A. guttatus is certainly the commonest large dragonfly encountered in Borneo and it frequents almost any deep standing water habitat in open country. Males in particular are active all the day and may be seen hawking up and down drains, across natural lakes, or around dams. The females tend to oviposit in the afternoon, often after dusk. Eggs are inserted into suitable soft living plant tissue, the underside of lily pads being a common choice. They are not overly difficult to capture as they fly quite low and in broad daylight. Nevertheless they are swift and powerful fliers and the best way to net them is to watch as they beat out a regular patrol and, once the flight paths are ascertained, lie concealed in ambush. This can be quite time consuming and sometimes seems scarcely worth the effort for such a common insect; hence they seldom appear in collections in large numbers. The mature larvae (Figs. 151 & 152) are disproportionately large, highly streamlined and highly aggressive. They often swim actively after prey, especially tadpoles. Very young larvae have a distinct banded pattern. Exuviae are frequently discovered clinging to waterside vegetation around ponds and dams. A. panybeus is very like guttatus, except that there is a distinct T' on the dorsal part of the frons, (the visible projection at the front of the head in the illustration), and the third abdominal segment is a little more constricted and distinctly longer. The male appendages also differ slightly. It is found in all the same situations as guttatus but is everywhere considerably rarer and more crepuscular in its habits.