Lestes Sponsa - Behaviour

Behaviour

One of the larger damselflies, this species is most common in July and August. It is often found by ponds and lakes, and is very rarely seen along flowing water. Emerald Damselflies like to perch among reeds, their colour providing good camouflage. They are not as strong fliers when compared to other common damselflies such as the Common Blue or Large Red Damselflies, but they are more likely to be seen on misty, rainy days then those species. When disturbed they usually do not fly very far away, landing on another perch a few yards away. Their habit of perching with their wings half open is characteristic of the family Lestidae and gives rise to their other common name of spreadwings. A population can consist of several hundred insects.

L. sponsa mate in the usual dragonfly manner and will form tandem pairs away from water. Copulation lasts from 30-60 minutes and after mating they stay paired for egg-laying. The female usually lays eggs in submerged vegetation and whilst egg-laying the female can remain submerged for 30 min. The female pierces the tissue of aquatic plants and inserts her eggs. Occasionally females lay their eggs in vegitation above the water surface in places that will become submerged when the water level rises. The eggs start to develop and will continue to develop for the next few weeks. Then due to changing environmental conditions the development of the eggs slows down. In this state of slow development, called diapause the eggs overwinter. L. sponsa is an obligatorly univoltine species.

The prolarva stage hatches from the egg in spring. This is a specialised short lived stage often lasting only minutes. The prolarva has no limbs and cannot feed but it can move by jumping or wriggling and if a prolarva is not in water when it hatches it will move about until water is found. Once in water the prolarva molt to the second stadia stage. The larvae are active and actively hunt prey leading to rapid larval growth. The larvae molt from one stadia to the next until growth is complete; in dragonflies the larval stages are the only stages where growth occurs. The number of stadia is not fixed and in good conditions the last larval stage, called F-0 can be reached in as little as 8 weeks.

The adults emerge in July and are on the wing until September. Adults are not sexually mature when they emerge and need a week or more, depending on conditions, before they can breed. In L.sponsa in Japan the length of the summer maturation period is correlated with temperature and lasts on average 20 days in the north where it is cooler up to 120 days in the hotter south. This stops egg laying early in summer, which could lead to egg not entering diapause and hatching in autumn. This would disrupt the normal cycle as larva hatched in autume would not survive the winter.