Species lugens (Hagen, 1861) [Agrion]
Head pattern of the mature male is obscured by heavy black pruinescence. In younger specimens the head appears tan with black markings and bears a pair of pale postocular spots separated by the occipital bar. The pterothorax is blue to tan with a thin black middorsal line and an additional lateral black line on each side contacting the middorsal carina above. The humeral stripe is black with a longitudinal stripe running down the middle of the mesepimeron. These stripes are often confluent at about 1/3 the length of the humeral stripe, isolating a pale spot anteriorly. In older individuals, the pterothorax darkens entirely and t he color pattern is obscured by pruinescence. The forewing has 5 or 6 postquadrangular cells. The abdomen is tan with black markings, becoming darker dorsally in mature individuals. Segments 1 and 2 are marked with black stripes extending the full-length of the segment dorsolaterally. The stripe widens apically on segment 2 to meet, or nearly meet, on the other side. Segments 3-7 are marked with a dark apical ring that covers 1/5-1/4 the length of the segment. and a dark lateral that is confluent with the apical ring. More mature individuals may have stripes more extensive dorsally. Segments 8 and 9 nearly all black in mature individuals with only a few pale spots. Segment 10 becomes dark in older individuals but usually retains pale color laterally. The cerci and paraprocts are only half the length of segment 10. The cerci are bifid with a pointed tooth on both lobes. The paraprocts each have a small black, dorsally-directed tooth on the apex of the superior lobe. Female coloration is similar to younger males, with dark markings less extensive. The lateral dark stripes are often contiguous with the middorsal carina as in males, but separated from any other black. The dark humeral stripe and stripe in the middle of the mesepimeron are sometimes as in the male, but are usually touching at their origin. The mesostigmal plates have distinctly diverging thumb-like posterior lobes. The mesepisternal tubercles are reduced the legs are generally pale with some dark markings on the femora. The abdominal pattern is similar to the male with dark stripes laterally on segments 3-7, widening apically to become confluent dorsally. The subapical spots on the lower sides are often contiguous with the narrow apical ring of each segment. There is a dorsolateral stripe on segments 8 and 9.
Total length: 41-50 mm; abdomen: 32-41 mm; hindwing: 25-35 mm.
Powdered Dancer (A. moesta ) is a little similar and mature males are almost white rather than black. Females lack additional dark stripes on either side of the middorsal stripe. Tonto Dancer (Argia tonto ) is bluer and lacks the additional dark stripes on the middorsum of the thorax.
Rocky, desert rivers and streams.
This species may be the most abundant damselfly at certain desert streams where it perches on emergent and marginal rocks. Despite this, its behavior has never been studied.
Southwestern U.S. and Mexico; Texas west to California and Oregon south to Veracruz.