|Common blue damselfly|
|young adult male|
|young adult female|
Enallagma cyathigerum (common blue damselfly, common bluet, or northern bluet) is a European damselfly. The species can reach a length of 32 to 35 mm (1.3 to 1.4 in). It is common in all of Europe, except for Iceland.
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. A male is blue while a female is brown on a common blue damselfly.
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.
This small, brightly coloured damselfly is probably the most common of dragonflies and damselflies throughout much of Britain. It inhabits a wide range of habitats, from small ponds to rivers. They are especially common at lakes and reservoirs. Once the damselflies are in tandem and perched, the female can swing her abdomen to initiate pairing.
This damselfly requires a close look for a beginner to distinguish them from an azure damselfly. Typically, they fly low through the reeds and often fly well out over the water, unlike azure damselflies. They are also a brighter blue.
- Azure damselfly, a similar looking species
- Ischnura heterosticta, a similar Australian damselfly
- List of British dragonflies