N 



688 CLASS IV. INSECTA. 



can be shot out with extreme rapidity to catch insect prey (Fig. 

 435). The alimentary canal in these instars is richly supplied 

 with tracheae and respiratory water is pumped in and out per 



anum, the action being at times 

 with such force as to propel the 

 nymphs forward. When there 

 is no air in the water the tail 

 \* is protruded from the surface 



FIG. 435. &schna larva with rudimentary and air IS taken ill by the 



wings and mask. . i t 



anus in the place or water. 



Dragon-flies sometimes migrate in large numbers, especially 

 the genus Libdlula. As a rule they frequent places such as 

 country-lanes, hedges, and the banks of streams, where they are 

 most likely to meet other insects, which they devour in large 

 numbers, catching them on the wing, and apparently entangling 

 them in their legs and then handing them on to the jaws. 

 The larvae and nymphs are also very destructive not only to 

 other insect larvae but to the fry of freshwater fish. They have 

 no sting and are quite harmless when caught, although there 

 are many legends to the contrary. There are some 2,000 

 species described and 4(3 of these are British. The order is 

 divided into two families and seven sub-families : 



Fam. 1. Anisopteridae. Front and hind wings dissimilar, win ITS when 

 at rest horizontal, eyes not pedunculated. 



Sub-fam. 1. Gomphinae. Eyes wide apart. Gomphns brilliantly 

 coloured : a primitive group. 



Sub-fam. 2. Cordulegasterinae. Eyes touching at one point only. 

 Cordulegaster ; the images have a regular " beat " when on the wing : 

 the nymphs burrow in mud. 



Sub-fam. 3. Aeschninae. Eyes in contact for some distance. A 

 large group both in size and number. Anax ; Aeschna ; Epiaeschna. 



Sub-fain. 4. Corduliinae. Eyes with a tubercle behind them. 



Sub-fam. 5. Libellulinae. No tubercle behind eyes. Abdomen 

 often prismatic in cross section. Libdlula. 



Fam. 2. Xygopteridae. Wings alike, when at rest vertical, eyes 

 pedunculated. Damoiselle- or Damsel-flies. 



Sub-fain. 1. Calepteryginae. Wings with at least o cross 

 nervures between the 1st and 2nd longitudinal nervtires. A 

 primitive group. Calepteryx haunts woods. Hetaerina ; Palaeo- 

 phlebia Japan, has Calepterine wings and a Gomphine body : Euphaea. 



Sub-fam. 2. Agrioninae. Wings with only 2 cross nervures 

 between the 1st and 2nd longitudinal nervures. Often small and 

 very delicate insects. Agrion ; Lestes ; Enallagma ; the tropical 

 species Mecistogaster and Megaloprepus exceed in length of body and 

 stretch of wing all other insects. 



