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.
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.
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