AQUATIC INSECTS 



Insects and their larvae are one of the most unfailing sources of food 

 supply for freshwater fishes. There are many, however, which in some 

 or all the st^es of existence are injurious to the spawn and young, and 

 these belong to many orders, families, genera and species, among 

 them being some genera of the Heteroptera or Water-bugs ; the Neurop- 

 tera or Dragon-flies and kindred insects; the Diptera or true Flies; the 

 Coleoptera or Beetles; the Lepidoptera or IMoths; the Hymenoptera or 

 Ichneumons; the Arachnidae or Spiders; and other families of the insect 

 world, or forms closely related thereto. 



Some are not entirely rapacious nor depend solely on the blood of 

 animals for food, but also suck the juices from insects and plants, yet be- 

 come active enemies in the confines of the rearing basins for fishes, in the 

 absence of larger fishes which would devour them and their larvse; thus 

 permitting them to prey upon the smaller fishes and to so increase in numbers 

 as to become very destructive. These will be briefly described, their 

 habits noted, and illustrations given for their identification. Others which 

 serve as food for young and mature fishes will also be mentioned. 



Freshwater plants grow in more or less shallow water, as they are 

 dependent for nutrition upon the decomposition of carbonic acid gas by 



sunlight, and as plant-feeding animals establish 

 themselves among them, they are also frequented 

 by predatory animals, to whom these serve as 

 food. Insects are of both these classes but the 

 predatory more particularly claim our attention. 

 It should be stated that insects deriving oxygen 

 from the air are generally lighter than water, 

 so that, should they exhaust the air carried with 

 them under the water or become disabled, they 

 rise to the surface by gravity in such position 

 that the air-breathing parts first come to the 

 surface. The insects deriving oxygen from the 

 air held in suspension in the water are heavier 

 than water and no effort is necessary for them 

 to keep below the surface. Changes in water 

 temperature are also provided against and most 

 of the aquatic insects pass the winter in the 

 larval stage, to undergo the further transforma- 

 tions in the following spring or early summer. 



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