Key to last instar larvae of Aeshna occurring in Mexico and the southwestern U.S.

1 Cerci with a row of 5–6 spiniform setae on lateral margins; total length of mature larva 49 mm ................................ ............................................................................................................................. williamsoniana (Mexico to Panama)

- Cerci without a well-defined row of spiniform setae, although with very minute spiniform setae on surface; total length of mature larva 34.0– 46.5 mm ..........................................................................................................................2

2 Labial palp tapering to slender, slightly curved apex; prementum length/maximum width 1.13–1.22; female gonapo- physes reaching posterior margin of sternite 10 or beyond .......................................................................... constricta

- Labial palp squarely truncated at apex; prementum length/maximum width 1.22–1.65; female gonapophyses reach- ing at most mid-length of sternite 10 .......................................................................................................................... 3

3 Prementum> 7.50 mm long; head width> 8.5 mm ................................................................................... persephone

- Prementum <7.50 mm long; head width <8.5 mm ................................................................................................... 4

4 Prementum length/maximum width 1.18–1.34; distal maximum width of labrum more than 3 times median length. ..................................................................................................................................................................................... 5

- Prementum length/maximum width 1.37–1.60; distal maximum width of labrum less than 3 times median length. 6

5 Cerci length/epiproct length 0.56–0.69; anterior lobe of supracoxal process markedly narrower than posterior lobe; midline of abdomen without a dark stripe ......................................................................................... interrupta interna

- Cerci length/epiproct length 0.73–0.80; anterior lobe of supracoxal process slightly narrower to nearly as wide as posterior lobe; midline of abdomen usually with a dark stripe......................................................................... palmata

6 Cerci length/epiproct length 0.69–0.77; head width usually 1.1–1.2 times prementum length. umbrosa occidentalis

- Cerci length/epiproct length 0.80–0.92; head width usually 1.2–1.3 times prementum length ....................... walkeri