THE HABITS OF NOTONECTIDAE 385 



undulata kill and suck the juices of young fish which had just 

 emerged from the eggs. I have seen the nymphs and adults kill 

 young Diemyctylus torosus as soon as they emerged from the 

 gelatinous envelope. I have also observed a nymph dragging 

 a Diemycty'us larva which was about three times its own size. 

 The nymphs usually attack May-fly larvae and drag them about, 

 although the latter are. twice the size of the aggressor. The larger 

 species usually attack the smaller ones and the young are eaten 

 by the adults, being seemingly preferred to other kinds of food. 

 Notonecta nymphs of equal age and size attack each other 

 and suck each others juices during their attack until one or 

 both are dead. They often attack dragonfly nymphs, which 

 are many times their own size, usually approaching from beneath, 

 grasping them with the forelegs and piercing the body with the 

 proboscis. The nymph has no chance of escape from the insect, 

 the latter continuing its hold no matter what position the victim 

 may assume. The dragonfly nymph does not die from the first 

 attack but only after a number of punctures. Notonecta is also 

 destructive to young fish. 



The Notonectidae are not easily affected by chemicals, as 

 they may live in strong sodium chloride solution without showing 

 any change in activity. They can live in five per cent alcohol 

 for days. They become drowsy in twenty per cent alcohol, but 

 if put in pure water they revive again. Several specimens were 

 kept in strong copper sulphate solution for several weeks and 

 did not suffer from it, while other animals dropped in the same 

 liquid died within a few minutes. A Notonecta insulata was 

 kept alive in Gilson's fixing fluid over two hours. 



Notonectas are positively phototactic and can be led by the 

 light in any direction. If an aquarium containing Notonectas 

 is left in the sunshine, the bugs move quickly to the lighted 

 end of the tank, and fly toward the light, producing a buzzing 

 sound. If the aquarium is placed between two lights of different 

 intensities, the Notonectas usually collect near the light of 

 greater intensity, as is shown in the following table: 



Two lights, one of one hundred candle power, the other of 

 thirty-two candle power, were placed one at each end of the 

 aquarium. Every five minutes the lights were reversed and the 

 insects moving toward each light counted. 



