Tetracanthagyna larva

An impressive larva I’m currently rearing has provided very fascinating insights into terrestrialism in dragonflies larvae.
This aspect of larvae ecology is rather well known. There are several studies showing larvae inhabiting small streams or seepages in forest can have a diminished dependence on water. Some species in Japan live among wet rock and mosses beside streams, a species in Himalaya hang around wet ferns near waterfalls and one species from New Caledonia clings onto the underside of moist leaves away from any water body.

Closer to home, larvae of the genus Tetracanthagyna exhibits semi-terrestrial behaviour. Tetracanthagyna degorsi from Borneo apparently leaves the water at night to perch head down near water surface, seemingly to catch surface swimming fishes. T. waterhousei is another species with similar habits. There’s a picture of its larva catching a fish while completely out of water in the Field Guide to Dragonflies of Hong Kong 2nd edition (page 211).

The larva I have now also shows identical behaviour. Its hunting strategy is ambush. Most of the time it clings out of water with only the head partially submerged. From this position it waits, and when a shrimp moves near, wham! The forceful impact of its labium capturing the hapless shrimp fatally.
After capturing, the larva will occasionally move completely out of water to consume the prey. I notice the bigger the shrimp, the more likely it’ll move above water for consumption. And this becomes more frequent as the larva grows.
Those with a phobia for things creepy and crawly will find this larva utterly hideous. It is now almost entirely black, having adapted its colour to the surroundings; it currently measures about 6cm in length; and has a dragon-like frontal appearance. It might look monstrous but once emerged into adult, it will become the biggest dragonfly in the world in terms of wingspan and weight.

Tetracanthagyna plagiata is the only species from the genus recorded in Singapore so this larva should be of the species. I didn’t have the chance to establish its gender accurately so hopefully it’ll emerge into a male as very few male specimens of T. plagiata exists in museums worldwide. It should emerge very soon as it has stopped feeding for the past few days.

Pictures taken at: ex-situ, November, December 2009 & January 2010.


References:

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

Norma-Rashid, Y., L. F. Cheong, H. K. Lua & D. H. Murphy, 2008. The dragonflies (Odonata) of Singapore: Current status records and collections of the Raffles Museum of Biodiversity Research. Raffles Museum of Biodiversity Research, Singapore. 24 pp. Uploaded 07 Nov 2008 [http://rmbr.nus.edu.sg/raffles_museum_pub/Dragonfly_of_Singapore.pdf]

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

Wilson, K. D. P., 2004. Field Guide to the Dragonflies of Hong Kong 2nd edn. Agriculture, Fisheries and Conservation Department, Hong Kong SAR.

Kopstein’s Bronzeback (Dendrelaphis kopsteini )

A recent survey at the Central Catchment turns out to be one of the best I’ve had this year. Rare creatures sighted, good weather and good companions made a perfect morning in the forest. We spotted three snakes that day. The stand out has to be this Kopstein’s Bronzeback (Dendrelaphis kopsteini).
Also known as Red-necked Bronzeback, this species has always been confused with Elegant Bronzeback (Dendrelaphis formosus). It was only in 2007 that scientists sorted out the taxonomy and designated it as a separate species. We now know Kopstein’s Bronzeback can be distinguished from other Bronzeback snakes by its bright orangey red colour at the back of its neck. The species is widespread locally, being also present in rural or suburban areas. Although widespread, it is considered rare by Baker & Lim (2008) and has a status of vulnerable in the Red Data Book. Its distribution is from Thailand down to Peninsular Malaysia and Sumatra.

We were very lucky indeed to chance upon this individual consuming a lizard. When we first saw it, it had already captured the prey. After a brief struggle, the snake proceeded with lunch, swallowing the lizard in a matter of minutes. Our presence did not bother it at all thus enabling me to get a close video. Spotting creatures in the wild is always great but a window into the midst of their daily activity is unquestionably a huge bonus.

Kopstein’s Bronzeback is named after the Austrian herpetologist Dr. Felix Kopstein (1893-1939).

Pictures and video taken at: Central Catchment Nature Reserve, November 2009.

References:

Baker, N. & K. K. P. Lim, 2008. Wild Animals of Singapore. A Photographic Guide to Mammals, Reptiles, Amphibians and Freshwater Fishes, Draco Publishing and Distribution Pte Ltd, Singapore.

Davison, G. W. H., P. K. L. Ng & H. C. Ho (eds), 2008. The Singapore Red Data Book: Threatened Plants and Animals of Singapore. 2nd Edition. The Nature Society (Singapore), Singapore.

Vogel, G. & J. Van Rooijen, 2007. ‘A new species of Dendrelaphis (Serpentes: Colubridae) from Southeast Asia’, Zootaxa 1394: 25–45.

Neurothemis fluctuans; Trithemis aurora

How do dragonflies recognise members of their own species? Recognition of conspecifc is primarily through visual cues for dragonflies. They can recognise flight style, size, colours and patterns as well as ultraviolet reflection and optical density. The ability to recognise their own species is important as it enables dragonflies to defend territory and for a male to find the right female.

But sometimes, mistakes do occur. On a recent sunny morning in Singapore Botanic Gardens, a whole lot of dragonflies were active. There was about six species present and the area was buzzing. It seemed like an orgy was taking place as males grasped females for copulation and inseminated females were ovipositing. The males were also fighting each other for the females. Suddenly a tandem pair crashed onto a plant. A male Neurothemis fluctuans had grasped a female Trithemis aurora. The pair made several attempts to fly off but failed.

Tandem link between different dragonflies species is prevented because of the incompatibility between a male’s anal appendages and a different female’s head. It is like a lock and key system; the right key must fit the right lock. In this case, it is obvious the male N. fluctuans couldn’t grasp the female properly. After several tries, the male realised its mistake and released the female.
Both Neurothemis fluctuans and Trithemis aurora are very common species here. Both species are sexually dimorphic. Mature N. fluctuans males are reddish while the females are light brownish. For T. aurora, mature males are pink while females are yellowish.

Pictures taken at: Singapore Botanic Gardens, 2009; Toa Payoh Town Park, 2009 & 2008.

References:

Corbet, P. S. & S. J. Brooks, 2008. Dragonflies. HarperCollins Publishers, London, UK.

Brown Tree Snail

Recently, the rarest land snail in Singapore was sighted in great numbers. They were all congregated on two trees in the Singapore Botanical Gardens (SBG), several of them mating with some observed among leaf litter. This is the Brown Tree Snail (Amphidromus inversus inversus).

This critically endangered snail is mainly arboreal, inhabiting trees within primary forests preferring humid and damp conditions. Only one population survives in Singapore, and that's in SBG. We are not sure how big the population is but I believe it is hanging on by a thread considering the snail is found only within a small area in SBG. My knowledge on land snails are limited so I wonder why its found only at SBG and not in our forest reserves too. As mentioned in the Singapore Red Data Book, a study on population size is long overdue and a concerted effort must be made to introduce a second population in the nature reserves.

We have five Amphidromus species and subspecies in Singapore. The other one that is also rare is the Green Tree Snail (Amphidromus atricallosus perakensis) from the nature reserves.
As I took the pictures, passerby walked past. Some gave me curious glances but most ignored me. Many Singaporeans don’t know we have several species of flora and fauna eking out a last stand here. Many of these species are unspectacular and inconspicuous unlike the charismatic Colugo or the iconic Oriental Pied Hornbills. The extinction of a snail would hardly make a dent in an urban dweller’s life. But it’ll be a loud silent scream from our natural heritage.

Snails in the pictures are individually marked for research purposes.

Pictures taken at: Singapore Botanical Gardens, August 2009.

References:

Lok, A. F. S. L. & S. K. Tan, 2008, ‘A review of the Singapore status of the Green Tree Snail, Amphidromus atricallosus perakensis Fulton, 1901 and its biology’, Nature In Singapore, vol. 1, pp. 225-230.

Davison, G. W. H., P. K. L. Ng & H. C. Ho (eds), 2008. The Singapore Red Data Book: Threatened Plants and Animals of Singapore. 2nd Edition. The Nature Society (Singapore), Singapore.

Orthetrum chrysis ; Larva Emergence

Although dragonfly larvae have been studied widely, this aspect of their life history still harbours unsolved mysteries. For example, there’s several dragonfly genus whose larvae are still unknown and not found or described. The best way to study larvae ecology is to rear them ex-situ. This requires patience, time and acquired knowledge through practice. Inspired by the excellent work by Dr. Ian Choong from Malaysia and encouragement from Yeh Wen-Chi in Taiwan, I decided to take on this challenge whole heartedly.

Two to three days prior to emergence, a typical larva will stop feeding and climb partially out of the water. This is when aquatic respiration slowly change into atmospheric respiration. Once ready it will leave the watery environment into an aerial existence. After rearing this larva for 20 days, a miracle of nature finally unfolded.
Tropical dragonflies mostly emerge at night to pre-dawn. There are four stages of emergence. The first is when the larva search for a suitable support, climbing upwards and away from water. At this stage, the cuticle is still intact.

At second stage. the cuticle of the head and thorax split with the adult now pushing itself out of the moult (known as exuvia in dragonflies). Looking at the process, I actually sensed the dragonfly’s physical exertion. Slowly, the head, thorax and legs emerged with only the abdomen still inside the exuvia. Normally, a dragonfly would then rest for a while.
When it has regained energy, it swung forward to hang onto the exuvia and pulled its abdomen out. This is the third stage. The dragonfly is now fully emerged but looks all wriggled and fragile.

Finally in stage four, bodily fluids are pumped throughout the body to expand the abdomen and wings and also gaining full colour. Just like an ugly duckling, its wings open and transformed into a beautiful reddish female Orthetrum chrysis.
The entire four stages require 1-2 hours. Sacrificing sleep from 4-6am to witness this event is certainly worth it. For a dragonfly, it now enters an aerial lifestyle of hunting, territorial fights and procreating the next generation.

Orthetrum chrysis is a common dragonfly. Although mostly encountered at forest margins, we can also find them in well-vegetated park ponds. Of the several red-coloured dragonflies in Singapore, males of O. chrysis can be recognised by its red abdomen and blackish-brown thorax.

Pictures taken at: ex-situ, May 2009 (larva and emergence); Bishan Park pond, September 2008 (adult male).

References:

Corbet, P. S. & S. J. Brooks, 2008. Dragonflies. HarperCollins Publishers, London, UK.

Silsby, J., 2001. Dragonflies of the World, CSIRO Publishing, Victoria, Australia.