Other than dashers and dropwings, parasols and baskers, the dragonflies one is most likely to encounter on streamside vegetation or the banks of suburban ponds belong to a group known as skimmers, a rather more fetching appellation than the straight-laced name bestowed upon the genus in 1833 by Edward Newman, an English entomologist who sought to split Libellulla, Linnaeus's epithet for all Odonata, into more meaningful branches. Those with a laterally compressed abdomen he christened Sympetrum (sympiezein=press together and ētron=abdomen in Greek), while others, having laterally parallel rear segments, he dubbed Orthetrum (orthos=straight).
The taxonomic utility of abdominal profiles would prove to be dubious, as species were soon found that defied their generic description, and many more appeared that fit the bill but bore no relation to the genus, which is defined by traits that include the following: no less than 12 antenodal crossveins, including a distal antenodal that extends into the subcostal space of the forewing; a non-metallic frons; a prothorax fringed with long hairs; and a closed anal loop. In the field, Orthetrum can be reasonably distinguished by their robust bodies, slender, tapering abdomens, shortish legs, largely hyaline (save a basal tint) wings with long, pigmented pterostigmas, and a preference for perching on flat or laminar surfaces with their torsos roughly level, rather than on the tips of reeds and emergent shoots.
The abdomens of the two red species that occur in Singapore, Orthetrum chrysis and O. testaceum, are also conspicuously broadened towards the base. Males of the latter, which can be told apart from the look-alike Crocothemis servilia by the lack of a dark dorsal line, frequent artificial marshlands and degraded pools, darting about in tireless pursuit of rivals or hovering above a mate as she flicks batches of eggs into silty banks. Spine-tufted skimmers, which favour less disturbed habitats, can be found in coastal woods as well as shady brooks by well-trodden trails, which they may share with forest-loving odonates such as Euphaea impar, Prodasineura humeralis and Trithemis festiva. A tuft of bristles on the second abdominal segment and a darker thorax separate chrysis from brick-toned testaceum, which also burns with a duller fire than its slightly smaller cousin.
Ochreous tones are, at least to odonatologists more familiar with European and African taxa, exotic hues for a genus associated with caerulean hues. As if to balance the spectral scales on the local front, Orthetrum glaucum and O. luzonicum offer a brace of blue that recall their near eastern kin, which similarly acquire a waxy cloak upon maturity. Glaukos is Greek for blueish green or grey, and the specific name certainly suits the common blue skimmer, a dragonfly that is said to hang around forest edges, even at some distance from water, but can also be seen clinging to the walls of hillside drains and rural clearings. Teneral females maintain a drapery of brown and dull yellow, but a powdery bloom coats of the bodies of both sexes as they age and the rigour of a life on the wing takes its toll on frayed and failing veins.
Slender blue skimmers stay close to waterbodies, where they dash from blade to blade, occupying the middle ground, as it were, between the dwarves of their order and giants that prey upon fellow odonates. The smallest local representative of the genus and similarly pruinose at maturity, Orthetrum luzonicum is noticeably more lightly built, sports sky blue, as opposed to greenish blue, eyes, and lacks the dark hindwing base of its glaucous congener. The only other libellulid that could be mistaken for them is Brachydiplax chalybea, but this species has a markedly stouter build and a predilection for more commanding perches, from which males survey their turf for matches and mates.
The final rogue in the native gallery, Orthetrum sabina, is a dragonfly in a class of its own, a wanderer matched only by Tramea and Pantala, and a voracious, at times exclusive, hunter of other odonates. At home in city parks, lowland swamps and volcanic slopes, and the dominant aerial predator on the beach at Lim Chu Kang, where sordid flies and jitterbugging sandhoppers feast on carrion and the discards of weekend fishermen, these monsters in green and black lord over habitats that have run aground, erupting in furious whirls under a grove of sea hibiscus trees and staking their claims on sun-soaked twigs that cast slim shadows over a flat of buried treasures.
Missing, or missed, if ever it was here, from this island of migrant hawkers is a skimmer which appears to be the result of a biogeographical cut-and-paste job. In Orthetrum pruinosum, a scarlet tail, far more fiery than those of chrysis and testaceum, sprouts from a body of violet-blue, resulting in an insect of striking contrast and rather more fastidious requirements than its other lowland cousins. Singapore, having lost its riparian fringes, offers no refuge for these bold flyers. In Borneo, Sulawesi and the Malay peninsula, however, these dragonflies abound in the unfelled interior, where they patrol bubbling streams, seeding their young in still side pools or the stranded beds of seasonal rivers, and squander the final, frenzied stage of their natural lives on manœuvres that hold no water and appeals to history that carry no weight.
Comments