

THE ANIMALS OF THE FRESHWATER AQUARIUM 117 



or stagnant pools, are limbless creatures which hang head down- 

 wards into the water, protruding the tail through the surface 

 film of the water. This tail contains respiratory organs adapted 

 for breathing air, so that you will notice that the gnat larva is 

 much less definitely aquatic than that of caddis or dragon-fly. 

 The hanging head enables it to seize food particles in the water. 

 If alarmed the larvae sink down below the surface ; soon, however, 

 it rises again by wriggling movements of the body. After several 

 moults the creature becomes a pupa, in which stage it can move 

 but not feed. The pupal skin then cracks, and the perfect gnat 

 emerges. It does not require any solid body on which to rest 

 during the process, like caddis or dragon-fly, for it thriftily utilises 

 the floating pupa skin from which it has just emerged, standing 

 on this until the drying of the wings enable it to take its flight. 



Instead of the gnat larvae the so-called blood-worms, which 

 are the larvae of a gnat-like fly called Chironomus, may be 

 studied. They live at the bottom in soft mud or decaying 

 matter, and their history generally resembles that of the gnat. 



In discussing some representatives of the insects which are 

 aquatic as adults, as well as in larval life, it will be necessary to 

 exercise an even more rigorous selection than in the case of the 

 larvae. The following have been chosen as good animals for the 

 aquarium, and also illustrate well the special peculiarities of 

 structure to be found among the aquatic insects. 



We may begin with Dyticus marginalis, a large and handsome 

 water-beetle, to be found in nearly every pond or ditch. It is 

 a true air-breather, and may be seen swimming through the pond 

 with great rapidity, and ever and again rising to the surface and 

 protruding the tip of its abdomen above the water in order to 

 take in a supply of air. It should not be introduced into an 

 aquarium containing delicate or defenceless animals, for it is a 

 most voracious feeder, and will attack animals much bigger than 

 itself. In captivity it will eat meat, raw or cooked," and should 

 be abundantly supplied with food. It has powerful wings, and 

 therefore the vessel in which it is placed should be covered, or 

 the captives may disappear in the course of the night, flying to 

 other more promising localities than that in which they find 

 themselves, or setting forth on a nocturnal search for a mate. 



