Species quadratum Selys, 1876 [Acanthagrion]
The eyes of males are black above fading to white below. The face is blue with varying degrees of black markings. They have large, distinctive, blue subcircular postocular spots outlined in black. There are generally pale spots visible lateral to each posterior ocellus. The middorsal carina varies from black to partly blue. The middorsal stripe is black and extends 2/5 to 1/2 the width of the mesepisternum. The antehumeral stripe is thin, blue and extends less than 1/2 the width of the middorsal stripe. The humeral stripe is wider and black. The remainder of the pterothorax is blue fading to cream ventrally. The legs are blue basally and pale distally with incomplete black stripes. The abdominal segments 1-3 and 7-9 are blue, while segments 4-6 and 10 are pale or cream in color. There is a black subquadrate spot dorsally on segment 1 and a black dorsal stripe extending the full-length of segment 2. The entire dorsum on segments 3-6 is black, with the exception of a narrow basal ring on each segment. The majority of segment 7 is black except for blue ventrolateral margins and its apex. The is a black vertical streak on segments 8 and 9 and segment 10 is black for half its dorsal length and highly elevated. The cerci are distinctively black and sloping downward at a 45-60o0 angle. The paraprocts are pale with black apically. The female has eyes that are brown dorsally fading to cream ventrally. The color pattern of the head and thorax are similar to the male but with the pale color more extensive. The mesostigmal plates are subtriangular with a distinct sulcus outlining the posterior margin. The middorsal carina bifurcates at about 1/4 its length from the anterior end. There are distinctive pits just behind the bifurcation. The legs are similar to the male, but with the black more reduced. The abdominal color pattern is similar to the male for segments 1-6. Segments 7-8 are black dorsally, except for pale basal and apical rings. Segment 8 is sometimes blue on the apical 1/4 of the segment. Segment 9 is blue dorsally and black dorsolaterally. Segment 10 is blue dorsally and yellow ventrolaterally, occasionally with a narrow black apical ring.
Total length: 29-33 mm; abdomen: 23-27 mm; hindwing: 15-18 mm.
Mexican Wedgetail is one of our few distinctive blue damselflies. Stream Bluet (Enallagma exsulans ) looks similar to females, but it has the postocular spots contiguous and a stockier abdomen.
Weedy ponds and slow backwaters.
This species has only been reported in the state from a few localities including the Lower Rio Grande Valley and the Devils River. It is a common species throughout most of its range and I anticipate that additional localities will be revealed in the south-central United States as more people continue to look at odonates.
Texas and Mexico south to Nicaragua.