« Previous Species | Next Species » | Photos
Big Bluet



Search For More Images

Enallagma durum

Hagen, 1861


Order Odonata
Suborder Zygoptera
Superfamily Coenagrionoidea
Family Coenagrionidae
Genus Enallagma
Species durum (Hagen, 1861) [Agrion]


Identification

The male's face is largely blue with a dark stripe across the front. The top of the head is a paler blue. The pale postocular spots are squared off and most often confluent with the occipital bar. The pterothorax is blue ventrolaterally. The middorsal carina is broadly pale blue, bisecting the entire length of the black middorsal stripe that is half the width of the mesepisterna. The blue antehumeral stripe maybe 1/2-3/4 the width of the middorsal stripe. The humeral stripe is black and narrows posteriorly but is 1/3-1/2 the width of antehumeral stripe at its widest. A black spot is present on the metapleural fossa. The rest of the pterothorax is blue, becoming much paler ventrally. The legs are pale, either tan or blue, with a black stripe on the outer femoral and inner tibial surfaces and the tarsi are pale and armed with black spurs. The abdomen is largely bright blue dorsally, fading to cream ventrally. The basal 1/2-2/3 of segment 1 and the apical 2/5-1/2 of segment 2 are black. Segments 3-6 each have an apical hastate black spot, that narrows medially, extending up to half the length of each segment. The entire dorsum of segment 7 is black, but the basal 1/5 is highly emarginated so that the black is narrowly confluent with the anterior segment margin. Segments 8-9 are blue and segment 10 is black dorsally. The cerci are tan becoming dark dorsoapically and relatively short, extending no more than a third the length of segment 10. Laterally, the cerci are truncated apically with a rounded posteroventral lobe. Dorsally, there is a pale internal tubercle visible. The paraprocts are pale with dark tips extending slightly beyond the cerci and appearing straight or slightly upturned. The female is either blue or brown. The head is marked as in the male, but with the black less extensive. The middle lobe of the prothorax lacks distinct pits. The mesostigmal plates are quadrate and deeply concave medially with a prominent posterior ridge. The pterothorax is similar to the male, but the humeral stripe is generally narrower than the pale antehumeral stripe. The legs are occasionally pale with black stripes. The apices of the tarsi and tarsal claws are dark. The abdominal pattern is generally similar to the male. The first segment is black dorsally for its entire length, with only a pale apical band. Segment 2 is black dorsally for its full-length with a slight lateral expansion apically at 3/4 of its length. Segments 3-7 are entirely black dorsally, but broadly emarginated basally. Segment 7 has a pale apical ring. Segments 8-9 are black dorsally each with an apical pale ring. Segment 10 is generally blue dorsally with a basal black spot extending rarely more than a third the length of the segment.

Size

Total length: 34-44 mm; abdomen: 28-35 mm; hindwing: 17-25 mm.

Similar Species

Although generally larger, Big Bluet may be confused with Familiar (E. civile ) and Atlantic (E. doubledayi ) Bluets. The pale postocular spots and occipital bar are nearly confluent in Big Bluet and generally separated by black in Familiar and Atlantic Bluets.

Habitat

Along the shores of lakes and rivers, often with brackish water and emergent vegetation.

Discussion

This species frequently inhabits brackish waters and seldom ventures far from the sea coast. It is considered to be one of the more primitive bluets because of its distinct venation and genitalia. Little is known about the reproductive behavior of Big Bluet. Females lay eggs head downward under water while males guard from perching sites above. It has been suggested that the large size of Big Bluet may be an adaptation to high winds on open lakes and shore lines.

Distribution

Eastern coastal species from Maine to Texas south into Tamaulipas Mexico.