Wednesday, September 05, 2007

Damselfly Metamorphosis

I noticed my first garden damselfly of the season on 02/06/07 as shown in the first photograph. This shows a freshly emerged immature adult, which is also known as a teneral. They are characterised by their shiny wings and the light pigmentation of their bodies.

The species name is Enallagma cyathigerum or the Common Blue Damselfly.

The following day I counted 8 of these damselflies in and around the garden, the majority of which were on my Carex grass, which is growing in the pond.

My wife, Bron, did a further investigation on the lower stems of the grass as they emerge through the waters surface. She noticed several shed larval skins known as the exuvia (plural exuviae). This is perfectly illustrated in the second photograph.

When the larva leaves the water, it is essentially no longer a larva as it is undergoing metamorphosis into adulthood. The metamorphosed larva climbs the stiff stems of emergent plants at the water's edge. When the insect is ready, it pumps fluids into its body causing it to swell and the larval cuticle to split. Emergence normally takes one hour for a damselfly, but it may be several more hours before the wing muscles are warm enough for the adult to take flight.