AQUATIC INSECTS OF FRESHWATER 



FIG. 197. Back-swimmer, Notonecta undulata. 

 Ventral and dorsal views. Enlarged. 



young fishes, weak flyers and clumsy of movement out of the water. In 

 Mexico the eggs of two species, C. mercenaria and C. femorata, are 

 collected in enormous quantities to be eaten by the Indians and are 

 exported in a dried state as food for birds, poultry and fishes. They are 

 distributed over the entire United States, the most general species being 

 C. undulata, C. interupta. Fig. 196, C. calva, C. alternata and C. vulnerata. 

 Back-swijwmers belong to the family of Notonectidse, of which 

 about twelve species of the genera Notonecta, Anisops and Plea are known 

 in the United States. Though greatly resembling the water-boatmen in 

 appearance and habit they are 

 more convex on the back, which is 

 keeled like a boat and on which 

 they swim with the ventral side 

 upwards and the hind end of the 

 body projecting to admit air beneath 

 the wings where the breathing 

 apparatus is located. The anterior 

 and middle legs are shorter than 

 the oarlike posterior legs, which are strongly developed for swimming. 

 The eggs are laid in incisions, pierced by the ovipositor of the female in 

 the stems of water plants. After hatching they rapidly pass through 

 the larval stage and assume the appearance of the adult. They are 

 predaceous and feed upon other water insects and small fishes, the power- 

 ful beak inflicting severe wounds to the fingers in careless handling. 

 They attack young fishes which are entirely devoured. The most gener- 

 ally distributed species are N. undulata, Fig. 197, N. insulata, N. irrorata, 

 A. platycnemis and P. striola. 



Water-Scorpions belong to the family of Nepidse and are so named 

 from the appearance of the anterior legs, of which the coxa are long and 

 the femor furnished with a groove into which the tibia and tarsus fits, 

 greatly resembling the hooklike cheUceres of the scor- 

 pion, and admirably fitted for seizing prey. The middle 

 and posterior legs are adapted for walking. At the 

 posterior end of the body two long half-tubes are de- 

 veloped, which when united form a tube for inhaUng air 

 when under water. The species of Nepa are fiat oval in 

 form, about one inch long, and the Ranatra long, 

 slender and twigltke, with all the legs thin and very 

 long, the body often attaining a length of 2 ^ to 3 inches. 

 The eggs are deposited in the stems of water plants 

 "^" 'tpalfuZaT''' and have long protruding filiments with probably pul- 



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