Rivers and streams vary according to geology, location, water quality and flow. However in relation to Dragonflies it is mainly the water quality and flow that are important. In Ireland rivers are not very good habitats for dragonflies and we have only two truly riverine species, the Banded Demoiselle Calopteryx splendens and the Beautiful Demoiselle C. virgo.
The Banded Demoiselle Calopteryx splendens is characteristic of slow moving rivers with silty deposits on the river bed. Where the water flow is reduced and the bottom is muddy, species that breed on ponds and lakes e.g. the Common Blue-tailed Damselfly Ischnura elegans, the Azure Damselfly Coenagrion puella and the Hairy Dragonfly Brachytron pratense can also be found.
Moderate to fast flowing rivers in mountainous areas are unsuitable habitats for dragonflies. Larvae that burrow cannot penetrate the hard, stony bottoms and there is little in the way of submerged vegetation, so species with larvae that are weed-dwellers are also absent. Riverine species have larvae that burrow or are good at clinging to the substratum to prevent being swept away by the current. The Beautiful Demoiselle Calopteryx virgo is found on rivers with a more moderate flow that have stony or gravelly beds.
|Nelson, B., Thompson, R. & Morrow, C., 2000 (October 5). [In] DragonflyIreland http://www.ulstermuseum.org.uk/dragonflyireland/|