INSECTS IN THE WATER 017 



If we attempt a rough classification of water insects, 

 we obtain the following table : 



Stages preceding the imago always aquatic ; 

 breathing dissolved air cutaneously or by 

 means of skills. 



Plecoptera (Stone-flits) 



Ephemeroptera (May-flies) 



Odonala (Dragon-flies) 



Trickoptera (Caddis-flits) 



Neuroptera . , . Larva aquatic in one family — viz. the alder- 



flies (Sialidie) ; breathing dissolved air by 

 means of gills ; but pupa terrestrial. 



Hemiptera , , . About one-third of the bugs (sub-order 



Heteroptera) are more or less aquatic in 

 all stages ; breathing atmospheric air. 



Colcoptera . , . About one-tenth of the beetles frequent 



water in one stage or another; some 

 aquatic in all stages ; breathing atmos- 

 pheric air or (rarely) dissolved air by 

 means of gills (e.g. Gyrimis larva) ; pupa 

 usually terrestrial. 



Diplera ■ ■ • , Less than a quarter of the two-winged flies 



are aquatic in stages preceding the imago ; 

 breathing atmospheric air or dissolved air 

 cutaneously or by means of gills. 



In addition to the above, the larvas of a very few 

 moths are aquatic. Some of them possess gills, while 

 others appear to obtain their supply of oxygen through 

 the skin. Among the latter, the caterpillar of the brown 

 china-marks moth (Hydrocampa nymphceata) may be men- 

 tioned. It is often very common in ponds, where it feeds 

 upon the floating leaves of water-lilies and other plants. 

 The female moths creep into the water to oviposit. At 

 first the young larva burrows into the substance of the 

 leaf, but in later life it constructs a case, using two oval 

 pieces of leaf fixed together with silk. By some means, 

 not perfectly understood, the caterpillar contrives to keep 

 the interior of its dwelling dry, so that it now lives in 

 air, although immersed in water, and breathes in the ordi- 

 nary way by means of open spiracles. 



We have already seen that some of the spring-tails 



