The Odouata or Dragonjlies of South Africa. 367 



AN AX (Leach, 1815). 



A cosmopolitan geuus of large, strongly built and beautifully 

 coloured species, more numerous in the Old than in the New World, 

 some of them very widely distributed. 



Probably Anax is of typical origin, and lias spread to higher 

 latitudes as a result of migratory power and facility of adaptation to 

 various conditions of environment, and on the assumption that a 

 sufficiently high water temperature is available in the period of larval 

 development. The writer's observations of Anax imperafor in Switzer- 

 land seem to indicate that this development is comparatively rapid, 

 being completed in one year, whereas Aeschna nymphs, as observed 

 by Dr. Walker in Toronto, Canada, by Dr. Wesenberg-Lund in 

 Hilleroed, Denmark, and )>y the writer in his Swiss home, need two, or 

 even three and more years to complete their larval life. Anax larvae, 

 as far as known, are living in the open water of ponds and small lakes 

 amongst aquatic vegetation and are consequently of the transparent 

 type, vividly coloured green or yellowish and with a highly cryptic 

 pattern. There is evidence that this mode of living in standing water 

 applies also to some of the most widely distributed Odonata of various 

 systematic groups {EtiaUagnia cyathigerum, Anax iniperaior &uA Junius, 

 Panlala fiavesceus, Tramea limbata). The conditions of environment 

 are very much the same for this type of larvae all over the world, 

 checks to Ije found only in the low temperature and in the competition 

 of other species of their own kind. The phenomenon seems a parallel 

 to the world-wide distribution of the aquatic plants themselves, among 

 which those larvae pa.ss their existence. Anax larvae are very swift in 

 movements and voracious feeders, as shown )iy their rapid growth. 



1. Thorax light green. No reel colour 2. 



Thorax brick red, with a greenish shade at the sides. Most of the body 

 venation and pterostigma brick red. Frons iuiniaculate . A. speratus. 



2. Abdomen in male light blue with a mid-dorsal sinuate, longitudinal black 



band; in female green with the mid-dorsal band ferruginovis to brown. 

 Frons with a broadly lanceolate or rounded basal black sjiot and a light 

 blue or greyish transverse band at anterior ridge 



A. imperafor niauncianus. 

 Abdomen mostly black with small light green spots ... 3. 



3. Very large species, with enormously long abdomen in male. Base of hind 



wings with a dark brown spot at tlie menibranule Frons with a broadly 



triangular basal black spot A.lristif:. 



Much smaller species. No blackish-brown spot at base of hind wings. 

 Frons with triangular black marks at base and anterior ridge, the two 

 spots narrowly fused A. georgms. 



