Variable Damselfly Coenagrion pulchellum
Because it is a quite variable species, it may be difficult to tell the Variable Damselfly apart from other blue damselflies. This is especially true compared to the Azure Damselfly. Often however it is sufficient to examine the markings on the second segment of the body of the males. This is shaped like a wine glass or a beaker. In the Azure Damselfly this is shaped like a U. And it is very uncommon for both species to appear at the same spot together. Do't forget there are many other blue species. Many of those are rare or local, for they are bound to specific environments. Should you be interested in correctly identifying damselflies and dragonflies look for good books or web sites.
The Variable Damselfly prefers standing waters with a lot of vegetation. It may be encountered along big lakes and small garden ponds. The larvae develop in the water in two years (sometimes one). This is an uncommon species in England and Wales and a rare species in Scotland. All over Ireland a very common, sometimes abundant species.