Species multicolor (Hagen, 1861) [Aeshna]
This is a common, predominately blue western species. The face, eyes and pale spots are all brilliant blue. The black "T" on top of the frons widens basally. The thorax has two pale blue lateral stripes that are nearly the same width for their entire length. The wings are clear with an abbreviated pterostigma surmounting 2-3 crossveins. The abdomen is long and strongly constricted behind segment 3. There is a low ventral tubercle covered with small spines on segment 1 and a middorsal tubercle on segment 10. There are the usual pale bl ue spots throughout its length. The male cerci are forked. Females may have blue or yellow-green thoracic stripes and abdominal spots.
Total length: 67-74 mm; abdomen: 45-52 mm; hindwing: 42-47 mm.
Male Arroyo Darners (A. dugesi ) look similar but lack the forked cerci and the anterior lateral thoracic stripe has a posterior extension at its upper end. Male Variable Darners (A. interrupta ) are generally more muted in coloration and have black line across the frons. Females of Paddle-tailed (A. palmata ) and Variable Darner lack a tubercle on the venter of abdominal segment 1. Arroyo Darner females are probably not reliably separated in the field.
Open sunlit areas of slow-flowing streams, sloughs, lakes and ponds, including alkaline ones, with moderate vegetation
This species is the most common darner found around still waters during the summer in the extreme western limits of the region. They tend to haunt almost any kind of standing water. I observed them so numerous around a Nebraska slough that I counted 21 individuals perched on a single twig during the heat of the day. Kennedy (1917 ) once commented on its abundance near civilization, writing in Sacramento, California, "This species was observed catching insects on the market street of the city at twilight, they flew among the wagons and buggies, entirely indifferent to numerous passers-by. This habit of familiarity with man's haunts is very noticeable in multicolor. It is the most domestic of all the western Odonata." It is widespread in our region and is known from east Texas.
Central and western North America from southern Alberta and British Columbia to Texas and California southward to Morelos, Mexico.