THEIR RELATION TO EACH OTHER 93 



mosquito wrigglers and display surprising skill in cap- 

 turing them. Others take in anything that comes along, 

 be it insect, crustacean, or even small pollywog or fish. 

 They have no aversion to their own kind and will eat 

 each other if food is scarce or not easily obtainable. 

 As for the adults, anything that comes within their 

 range will answer as prey ; but in general small flies are 

 the most abundant victims. The common name "mos- 

 quito hawk" indicates one common article of food, 

 and there is no doubt that a very large number of 

 specimens is eaten. In some cases the mosquito pest 

 may even be materially lessened by them during the 

 period of adult flight; but they scarcely rank among 

 the really controlling " checks because they are active 

 only during the day while the mosquitoes prefer the 

 night for their flight; and the dragons prefer the open 

 sunlit area around ponds or along streams, while those 

 mosquitoes that fly at all during the day prefer shel- 

 tered, shaded and darkened places. Most of the dragon 

 flies are simply general predatory feeders on any soft- 

 bodied insects which they can overtake, rather than 

 specific enemies of any one form. 



In the order Hemiptera there are no parasites on 

 insect life. The lice, parasitic on vertebrate animals, 

 are elsewhere considered, and nowhere else do we find, 

 in this order, any approach to true parasitism. Of 

 predatory forms there are a large number; indeed 

 among the aquatic species the majority are predatory, 

 feeding on other water insects and even fish. Among 

 these the little Corisidce and N otonectidce , water-boatmen 

 and back-swimmers, are especially vicious and active, 

 easily forming a very notable factor in the control of 

 aquatic insect life. 



Among the terrestrial forms the entire series Hom- 

 optera lacks predatory types; in the Heteroptera we 



