890 FRESH-WATER BIOLOGY 



sallies from one resting place to another, and alighting oftener on 

 stones or other flat surfaces than on vertical stems. 



The damselflies are not such good flyers. The common black- 

 wing Calopteryx (Fig. 136 1) may usually be seen fluttering gaily 

 about the borders of creeks, but most damselflies are Httle in 



Fig. 1360. The Blue Pirate dragonfly, Pachydiplax longipennis. (Drawn by 

 Mrs. J. G. Needham.) 



evidence, and confine their locomotion to flitting from stem to 

 stem amid the shelter of vegetation. 



The dragonflies eat other insects in vast numbers and in great 

 variety. A large part of their food consists of small diptera: and 

 because many of these small diptera are noxious species, mos- 

 quitos, etc., an extended inquiry was once made as to the feasibiUty 

 of using dragonflies to remove these pests : it appeared that dragon- 

 flies are not at all discriminating in their feeding, and wiU as readily 

 eat useful as noxious species. Then, too, they eat other dragonflies, 

 apparently preferring forms that are only a little smaller than them- 

 selves. Hagenius, for example, eats Gomphus, and Gomphus eats 

 Mesothemis, and Mesothemis eats Lestes, and Lestes eats Argia, 

 and Argia eats Ischnura, and so on from the greatest even unto the 

 least of them. 



Many dragonflies are eaten by birds and other animals at their 

 transformation, before they are able to fly and escape; and some 

 of those that are not very strong-flying are eaten habitually by 

 birds — the smaUer Libellulines by king-birds, and the smaller 

 damselflies by swallows. But it is doubtful whether anything that 

 flies is able to capture in flight one of the swiftest dragonflies. 



