A third species, E. lindenii (Blue-eye) has been added due to similarities in the genes, but more obvious also in behaviour and the males upper appendages, with the two other species. As this species does not have red eyes, the name Brighteyes has replaced the name Red-eyed Damselflies. 

The two Redeye-species looks a lot like Bluets (Coenagrion and Enallagma species), but they are all black on top of backside of the head. Only young individuals may have faint postocular spots. The Blue-eye has very narrow postocular spots, compared to Coenagrion, but also compared to Enallagma cyathigerum, which it probably resembles most. 
 
 

Erythromma najas (Hansemann, 1823) is a member of the damselfly family Coenagrionidae. It is one of the two European species with red eyes and with a body without a dominant red colour (for males, females have brown eyes). The thorax and the two last segments of the abdomen (S9 and S10) are bright blue. Males do not show antehumeral stripes on the upper side of the thorax, they are limited on females. The other segments of the abdomen are a dull greyish colour.

The male resembles blue-tailed damselflies (Ischnura species) but is distinguished by its large, spaced eyes that are a deep red. It is very similar to the Small Red-eyed Damselfly (Erythromma viridulum). This last species, which is a slightly smaller size, emerges about one month later. Its geographical range extends more southwards. It shows antehumeral stripes, a shiny abdomen with blue colour on the sides of abdomen's segments S2 and S8 (this area is greyish on the Red-eyed Damselfly). The upper side of the legs is often a pale colour (it is dark greyish on the Red-eyed Damselfly). 
 

E. najas and E. virulum looks very similar, but they differ both in size and extend of black markings on the abdomen of the males. In the picture bottom right, the faint antehumeral stripe (on top of the thorax) of E. virulum is seen, a stripe which E. najas lacks. 

Male E. najas (top) and E. virulum (bottom). The two males are vey similar, but the former is a larger and a more stout species. The dark patterns on the top of the abdomen differs, as E. najas is all dark on the 8th segment and all blue on the 9th and 10th. 

On the top of the 10th segment E. virulum has a dark x-marking, and it is seen how the 8th is blue up on the sides, and only black on top. 

The females of E. najas and E. virulum differ in that the former has an incomplete antehumeral stripe, and the latter a complete stripe. 
 
 
 

Legs black and yellow, or black and brown (the undersides of femora and coxae yellowish brown). Thoracic antehumeral stripes present (these short and anterior, in the female), or absent (the thorax entirely black, in the male); red to brown (reddish brownish). The wings held vertically in repose; similar in shape and venation; petiolate; unpatterned and clear. The inner wing venation blackish. Discoidal cell a simple quadrilateral, not longitudinally divided (trapezoid, without transverse veinlets). The wings exhibiting 4-5 psqs cells between the quadrilateral cell and the subnodus. Antenodal veins in the forewings 2. Pterostigma present; elongated but only about about twice as long as wide; light brown. The hindwings with two rows of cells distal to the pterostigma between the costa and the radial vein. 

Abdomen linear from a conspicuously swollen base; 25-30 mm long; predominantly dull black (and pruinosed blueish grey, in the male), or green to bronze, or black (greenish bronzy-black in the female); predominantly transversely banded (segments 1, 9 and 10 blue in the male only, the female with thin blue bands between segments 8 and 9, and 9 and 10; and both sexes with thin yellow bands between the other segments); without mid-dorsal spots. The male abdomen without auricles on segment 2; with paired inferior anal appendages. Abdominal segment 8 of the female without a ventral apical spine. 

Found in lakes, gravel pits, canals and slow-flowing rivers. The males often sit on water lily leaves defending their leaf from allcomers. Males typically spent much of their time perched the leaves of floating vegetation such as water lilies or mats of algae.
 
 
 
 
 

The nymphs elongate and slender-bodied, gradually tapering posteriorly; when mature, 29-32 mm long. 

The antennae with the scape considerably shorter than the other segments taken together; with the first flagellar segment longer than the pedicel. The mask narrowed gradually to the hinge; without a median cleft. The prementum bearing 6-8 major setae (3+3, 4+4, to 3+5). The body of the labial palps bearing 6-7 major setae. The outer margins of the labial palps without spines. Distal margins of the labial palps crenate and coarsely toothed. The moveable hooks of the labial palps without setae. The apical combs of the tibiae mainly of trifurcated setae. 

The abdomen terminating in three conspicuous caudal gills. The three caudal appendages all lamellar. The caudal lamellae blunt; with transverse dark bands (three, postnodally); hairy on both margins to beyond the middle; nodate, with the marginal hairs coarser proximally to the node and finer beyond it; with much-branched primary tracheal branches leaving the main trunk at an upward angle. The gizzard with 8–16 radially symmetrical folds. 

Adults on the wing early May to early October (generally in best mature condition late May to early August).