INSECTS 



25 



SOME WATER INSECTS. 



CHARLES C. ADAMS, 



IN field and forest bright-colored and 

 active insects attract our attention. 

 Aquatic insects, on the other hand, do not, 

 as a rule, possess such bright colors as 

 their land relatives nor move about with 

 as great rapidity, yet it does not follow 

 that they are less interesting. 



As would be expected, some of the 

 most interesting things about these ani- 

 mals are connected with modifications of 

 their form which have resulted from their 

 aquatic life. It is believed that the ances- 

 tors of water insects have been land in- 

 sects which invaded the water and have 

 thus become greatly modified in their new 

 surroundings. Locomotion and breath- 

 ing, either one or both of these functions, 

 are, as a rule, very different in land and 

 water insects. 



The variety of aquatic insects, if we 

 consider only the adults, is not great 

 when compared with the land insects. But 

 when we compare fresh and salt water 

 forms it is surprising how few kinds there 

 are which live in the sea, in spite of its 

 vast area and great food supply. So few 

 are the insects found in the sea, or other 

 salt waters, that, to most of us, to speak 

 of aquatic insects only calls to mind fresh 

 water forms. We shall, therefore, refer 

 almost wholly to fresh water forms. Let 

 us consider briefly a few examples of 

 these. 



We may distinguish two general 

 groups, according to their special habitat. 

 Belonging to the first group are those in- 

 sects which frequent, primarily, the sur- 

 face of the water. These forms which 

 breathe air directly, and not air dissolved 

 in water, as is the case with many other 

 water insects, must he, kept dry and be 

 able to maintain their position on the sur- 



face of the water. Surface insects, such 

 as the Water-Skaters, found on quiet 

 ponds and streams, and their marine rela- 

 tives, Holobates, accomplish this by 

 means of fine hairs which cover the feet 

 where they touch the water. The same 

 physical principal is involved here, as 

 when a needle or wire is floated upon 

 water, — that of surface tension. 



The fine hairs on the body of a water 

 insect act in the same way as those on the 

 feet, and thus keep the insect dry when 

 below the surface. These insects are thus 

 able to breathe as land insects, on account 

 of their being on the surface, and conse- 

 quently their respiratory systems are not 

 as greatly modified as in many of the in- 

 sects living beneath the surface. It must 

 be borne in mind that an insect breathes 

 by means of the air which enters the body 

 by small openings and is led by means of 

 tubes, which become very finely divided, 

 like veins, to all parts of the body. By 

 means of contractions and expansions of 

 the body of the insect, the air within these 

 tubes is caused to circulate, and thus im- 

 pure air is driven out and a fresh supply 

 is pumped in. 



Two of the commonest of these surface 

 dwellers, so well known to the small boy 

 who frequents ponds and streams, are the 

 Whirligig-beetles or Lucky-bugs, and the 

 long-legged Water-striders or Water- 

 skaters. 



The Whirligig-beetles are easy to rec- 

 ognize on account of their characteristic 

 circular gyrations when disturbed, and by 

 their habit of associating in large numbers 

 in quiet places. When one of these 

 groups is disturbed they exhibit such ac- 

 tivity that they well deserve their name, 

 "Crazy-bugs." The eyes of these beetles 



