Common Blue Damselfly

Common Blue Damselfly – Enallagma cyathigerum

European common name: Common Bluet

BDS pronunciation: enn-al-lag-mah sigh-a-thidge-er-um

The Common Blue Damselfly – Enallagma cyathigerum, is easily missed unless they are moving, and the female occurs in several colour forms that can make identification more difficult.

Classification:

Odonata
	Zygoptera		Damselflies
		Coenagrionidae	Blue or red Damselflies

An abundant damselfly, one of several similar species with blue and black markings.

The thorax features broad shoulder stripes and are the best way to positively identify them.

The male has a predominantly blue body with black markings and features a characteristic mark on segment 2, usually described as ‘lollipop’, ‘mushroom’, or ‘club’ shaped. The upper surface of segments 8 and 9 are entirely blue in males, with blue and black markings along the rest of the abdomen. The immature male is a paler, almost grey-violet, blue, but otherwise resembles the mature male.

Females occur in 2 colour forms: blue and drab. Both forms share the same markings. The drab form undergoes a colour change as it matures; first appearing straw coloured and becoming greener with age. Females have a prominent spine on the underside of segment 8, not found on other species in the region apart from the Blue-tailed Damselfly – Ischnura elegans.

Overall length: 29 – 36 mm
Wings: 18 – 20 mm

The broad shoulder stripes of the Common Blue are characteristic identifiers, but there are several other broadly similar species that might cause some confusion:

White-legged Damselfly – Platycnemis pennipes
Larger, paler colouring, white legs, black is less extensive on dorsal segments. Four shoulder stripes that are narrow, rather than two broad stripes.
Azure Damselfly – Coenagrion puella
The male features a characteristic ‘U’ marking on segment two, compared to the ‘lolipop’ found on the Common Blue. Male and female have narrower shoulder stripes. Segment two of the female is less dark, but overall the dorsal surface of the abdomen is more black than in the Common Blue.
Red-eyed Damselfly – Erythromma najas
The male has very obviously red eyes and the dorsal surface of abdomen is mostly black, with a blue ‘tail-light’. The female has a dark abdomen, with narrow or even incomplete shoulder stripes.
Small Red-eyed Damselfly – Erythromma viridulum
Smaller. The male has very obviously red eyes and the dorsal surface of abdomen is mostly black, with a blue ‘tail-light’. The female has a dark abdomen and a blue thorax with narrow shoulder stripes.
Blue-tailed Damselfly – Ischnura elegans
Dorsal surface of the abdomen mostly black, except for a prominent blue ‘tail-light’ (other colours in some female colour forms). Narrow shoulder stripes, which may be absent in some female colour forms.

Large ponds, lakes, gravel pits and slow rivers, with submerged vegetation used as ovipositing sites. Frequents vegetation away from water when not breeding.

Very common at rivers and lakes throughout the county, looking out over large bodies of water, such as those at Felmersham NR or Priory CP, they form a moving blue haze as huge numbers of them hover over the water in search of ovipositing sites.

Visible between mid-May and early October, peaking June to August.