Rhyothemis phyllis

A large swarm of Rhyothemis phyllis was encountered recently. There was at least 50 or more individuals flying around within a small opening in the forest. This species is known to form large swarms where they engage in rather slow, gliding midair foraging. Aggregation of foraging dragonflies has been well reported by odonatologists. In fact mass swarms like this occur more often in lee situations where there is shelter from wind.

R. phyllis is one of the most commonest species and very easily recognised by its wing patterns. A close up shot allows me to examine the intricate details of its wings. In terms of aerial versatility and agility, dragonflies probably stand at the peak of flight evolution among the insects or even some birds. Two wing structures play a key role. The nodus helps in the elastic tension thus allowing strong twisting and also as a shock absorber. The pterostigma at the distal edge on the wings provides favourable pitching moments during wing flapping acceleration. This then raises the critical gliding speed where self-excited vibrations take place therefore enabling a more efficient wing stroke with less power expenditure.

While out on survey work, I’m always the one chasing after dragonflies. So it was a good change to have dragonflies flying all around me uninhibitedly.


Picture and video taken at: Western Singapore, January 2007 & April 2008.

References:

Corbet, P. S., 1999. Dragonflies: Behaviour and Ecology of Odonata. Cornell University Press, New York.

Norberg, R. A. 1972. ‘The pterostigma of insect wings, an inertial regulator of wing pitch’, Journal of Comparative Physiology A: Neuroethology, Sensory, Neural, and Behavioral Physiology, vol. 81 (1), pp. 9-22.

Orr, A. G., 2003. A Guide to the Dragonflies of Borneo. Their Identification and Biology, Natural History Publications (Borneo) Sdn. Bhd, Malaysia.

Tyriobapta torrida

Females of different dragonfly species have different ovipositing modes. Scientists classify the different modes into three broad categories: endophytic (oviposition inside plants), exophytic (oviposition on anything except plants, which is water or substrate) and epiphytic (ovipositing on plants).

I’ve seen females ovipositing several times while out in the field. The most recent encounter gave me a chance to record videos of a particular female ovipositing in ultra speed mode.

This is the female of Tyriobapta torrida. She was flying in a circular motion at high speed and using the trajectory force to project water droplets and her eggs onto the water edge. Its amazing how fast she was flying and I can only imagine the aerodynamics involved. The lift and drag forces must be rather intense as well as the wings locomotion in overdrive to maintain the flight pattern. Not only that, she was going at it for almost 7-8 minutes. This is a lot of energy expended to produce the next generation. If only I can view this video in slow motion, which will certainly give an insight into the flight mechanics.

All the while, the mate-guarding male was hovering nearby. T. torrida males are easily recognised by the dark iridescent patch on the hind wing base. This species is rather common in our forests. T. torrida is the largest species within its genus. Where they occur, they are usually abundant with several individuals occupying and disputing small territories. Sexual activities are known to peak at around noon.

Corbet’s book described females from some other species diving underwater and ovipositing while submerged. Some species have been recorded to descend down to 1m depth. Now that is really a sight I want to behold.

This post is dedicated to Professor Philip Corbet who passed away on 13th February 2008 aged 78.


Pictures and videos taken at: Western Singapore, October 2007 & Venus Trail, March 2008.

References:

Corbet, P. S., 2004. Dragonflies: Behaviour and Ecology of Odonata. 2nd edition, Harley Books, Colchester.

Orr, A. G., 2003. A Guide to the Dragonflies of Borneo. Their Identification and Biology, Natural History Publications (Borneo) Sdn. Bhd, Malaysia.

Orr, A. G., 2005. Dragonflies of Peninsular Malaysia and Singapore, Natural History Publications (Borneo) Sdn. Bhd, Malaysia

Robber Fly

I was on Petai Trail recently and chanced upon this weird insect perching on a twig. It was motionless and thus perfect for a macro shot. It is about half the size of a palm and at first sight, looked rather fragile with its long abdomen hanging in mid-air. The poor insect seemed to be hanging for dear life.

It was only after I took a closer look at the picture and identification by Yixiong that I realised I’ve caught a glimpse of a fearsome predator of the insect world.

This is a Robber Fly from the Order Diptera (true flies). True flies are distinguished from other flying insects by having only a single pair of wings while their hind wings are greatly reduced into flight balancing organs called halteres. Robberflies belong to the Asilidae family but we are not sure what this particular species is.

Taxonomic classification aside, it is the ecology of robber flies that’s really fascinating. They prey on all sorts of insects, from easy ones like butterflies to prey that can put up a good fight like wasps, bees, spiders and dragonflies. In fact, some species are specialist hunters who target specific prey. Upon successful capture, a robber fly will inject its prey with saliva containing neurotoxin and other enzymes which immobilise the prey and liquify the tissue. Thereafter, the robber fly will suck on the soupy meal.

Not sure how well robber flies are studied in Singapore. But unsurprisingly, there’s tons of information on the web. This website http://www.geller-grimm.de/general.htm is one of the more comprehensive.

Pictures taken at: Petai Trail, March 2008.

References:

Geller-Grimm, F., T. Dikow & R. J. Lavigne. Robber Flies (Asilidae).
http://www.geller-grimm.de/asilidae.htm

Voluta nobilis

The second episode of Once Upon A Tree: Tides and Coastlines brought us back to nostalgic Singapore. Those were the days when people live much of their lives connected to the sea, for work as well as for play.

Work because, for example, The Raffles Hotel once stood just by the beach and would even be flooded during times of extreme high tides. Play, because trips to the sea then mean clear water, good fishing and excellent exploring on the seashore. The elders interviewed on the show mentioned big corals, huge fishes and dolphins were a regular sight. I’m quite sure one of the creatures they would have seen often too is this magnificent seashell, Voluta nobilis.

Voluta nobilis or “kilah” in the local language was once very common. They are now rarely encountered but still exists, mainly on our offshore islands. This pretty individual was spotted at Pulau Semakau recently. It’s been a while since I saw a live one, most of the time I found them as empty shells inhabited by hermit crabs. This individual’s siphon was fully extended as it searched for prey like bivalves. It will use its huge foot to suffocate and force its prey to open their shelves for oxygen. Once that occur, then its mealtime for V. nobilis.

Perhaps the elders from the documentary would be glad to know “kilah” can still be found in our waters.


Pictures and videos taken at: Pulau Semakau, February 2008.


References:

Tan, K. S. & L. M. Chou, 2000. A Guide to Common Seashells of Singapore. Singapore Science Centre, Singapore

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Diplacodes nebulosa; Rhyothemis triangularis; Lesser Whistling-duck

Another odonate survey with the gang, this time to the ponds of Marina East. The habitat is dominated by thin grass-like vegetation. Not very sure what plant it is but most probably belongs to the Cyperaceae family. The water itself is full of brownish algae and there’s a slight smell typical of eutrophic waters.

Nevertheless, this is an excellent habitat for odonates. They are in high abundance and are very active thanks to the warm morning sunshine. The most numerous species is Diplacodes nebulosa. They are very distinct due to the dark tips on their wings. All the males are defending a small territory and chasing each other, zipping all over the water surface.

The most striking dragonfly there has to be Rhyothemis triangularis, aptly named due to the deep metallic blue triangular patch on its hind wings. Dragonflies from the genus Rhyothemis characteristically have short abdomens with broad hind wings. Some of them are quite common in open countries or streams in swampy forest. R. triangularis is common and widespread in Asia. However in Singapore they are rather uncommon as habitats akin to the Marina East ponds are few and far between.

But odonates are not the only creatures inhabiting the ponds. From afar, a Lesser Whistling-duck (Dendrocygna javanica) made an appearance. This is a nationally vulnerable bird. Once again habitat loss is the main cause as freshwater ponds are destroyed when urbanisation encroaches. This bird has an estimated population of 250 in Singapore.

As we left Marina East, I sensed a “melancholy in the wind and sorrow in the grass” (Charles Kuralt). How much longer will this location remain as it is? Its neighbour at Marina South is already morphing into the Integrated Resort. Rumour has it that Marina East will become a golf course. “Another golf course?!” Tang sighed.

Perhaps we could get the developers to build the golf course while preserving this small nature haven? My mind begins to sparkle…




Pictures taken at: Marina East, January 2008.


References:

Orr, A. G., 2005. Dragonflies of Peninsular Malaysia and Singapore, Natural History Publications (Borneo) Sdn. Bhd, Malaysia.

Wang, L. K. & C. J. Hails, 2007. ‘An annotated checklist of the birds of Singapore’, The Raffles Bulletin of Zoology, Supplement 15: 1-179.