Pseudagrion microcephalum; Ceriagrion cerinorubellum; Ischnura senegalensis; Pseudagrion australasiae; Podolestes orientalis; Euphaea sp.

It is easy to recognise the larvae of damselflies. Compared to a typical dragonfly larva they are slimmer and less robust. More notably, damselfly larvae have three very distinctive caudal lamellae, also called external or larval gills, at the end of the abdomen. These are absent in dragonfly larvae.

The caudal lamellae have a variety of functions. They aid in respiration, function as fins during motion and can even break off in times of escape much akin to the discarded tail of a fleeing gecko. And just like a gecko’s tail, a larva can grow back its lost lamellae. The lamellae aid, but are not essential in respiration. Thus it is not unusual to see larvae missing one, two or even all of its lamellae just like the larva of Pseudagrion microcephalum below.
The shape and size of caudal lamellae will change as a larva grows. In many species, the lamellae will become smaller relative to abdomen length but expanding in width and more tracheated, hence having a bigger role in respiration.

Size, length, shape and patterns of caudal lamellae are essential tools in identifying species. Most damselfly larvae have lamellae which are flat and vertical like those of Ceriagrion cerinorubellum, Ischnura senegalensis and Pseudagrion australasiae. The brownish spots on the lamellae of C. cerinorubellum are examples of patterns which can occur.

Meanwhile, damselflies of the Euphaea species have their caudal lamellae in the form of swollen saccoids with a terminal filament.

Recently larva of the damselfly Podolestes orientalis is described. The species is from the family Megapodagrionidae and members from this family have their caudal lamellae in a horizontal plane. This character is unique to the family although not all species in the family have horizontal lamellae. I find the fan-like shape and banded patterns of P.orientalis lamellae very eye-catching. The larvae are now known to inhabit submerged leaf litter at the edge of shallow pools where they raised their abdomen upwards and have their lamellae splayed near the water surface. In this way, horizontal lamellae may be better adapted to aid respiration near the water surface in an otherwise low oxygen leaf litter forest pool. P. orientalis is a rather common species in our forests.

The larvae of many odonate species remain unknown and undescribed. Further discoveries will help scientists shed more light on the evolutionary history of this wonderful insect group.

Pictures taken at: Ex-situ, June 2009; September 2009; October 2009

References:

Choong, C. Y. & A. G. Orr, 2010, ‘The larva of Podolestes orientalis from West Malaysia, with notes on its habitat and biology (Odonata: Megapodagrionidae)’, International Journal of Odonatology, vol. 13(1), pp. 109-117.

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

Kalkman, V. J., C. Y. Choong, A. G. Orr & K. Shutte, 2010, ‘Remarks on the taxonomy of Megapodagrionidae with emphasis on the larval gills (Odonata)’, International Journal of Odonatology, vol. 13(1), pp. 119-135.

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