The Common Blue Damselfly can be easily mistaken for the Azure Damselfly (Coenagrion puella), but on the back and the thorax, the Common Blue Damselfly has more blue than black; for the Azure Damselfly it is the other way around. The second segment of the thorax has a distinctive spot with a line below connecting to the third segment.
Another difference can be observed when inspecting the side of the thorax. The Common Blue Damselfly has only one small black stripe there, while all other blue damselflies have two.
During mating, the male clasps the female by her neck while she bends her body around to his reproductive organs – this is called a mating wheel. The pair flies together over the water and eggs are laid within a suitable plant, just below the surface.
The eggs hatch and the larvae, called nymphs, live in the water and feed on small aquatic animals. Nymphs climb out of the water up a suitable stem to moult into damselflies.