1 86 AN INTRODUCTION TO ENTOMOLOGY. 



into bundles, which are then floated in the water of a lake until cov- 

 ered with eggs. The bundles are then taken out, dried, and beaten 

 over a large cloth. The eggs being thus disengaged, are cleaned and 

 pounded into flour." (Glover.) 



Family XII. NOTONECTID^E.* 

 (Back-swimmers or Back-swimming' Water-boatmen^) 



The Notonectidce differ from all other aquatic Heteroptera by the 

 fact that they always swim on their back. And there is a corre- 

 sponding difference in the form of the body. This is much deeper 

 than in the allied families, and is more boat-shaped. 

 The back, from the peculiar attitude of the insect 

 when in the water, corresponds to the bottom of a 

 boat, and is sloped so as to greatly resemble in 

 form this part (Fig. 157). 

 FlG> undui%a ect * The eyes are large, uniform, twice sinuated 



on the outer side, and project a little way over 

 the front margin of the prothorax. The prothorax has the 

 lateral margins sharp and projecting. The legs are all long ; the 

 hind pair are much the longest and fitted for swimming. 

 The tarsi consist each of three segments, but the basal segment 

 is so small that it is often overlooked. There is a ridge along the 

 middle line of the venter which is clothed with hairs. 



These insects are predaceous, feeding upon insects and other 

 small animals. In collecting them, care must be taken or they will 

 inflict painful stings with their sharp and powerful beak. 



The favorite attitude of the Back-swimmers is floating at the 

 surface of the water, with the caudal part projecting sufficiently to 

 admit of the air being drawn into the space beneath the wings. 

 When in this position, their long oar-like hind legs are stretched out- 

 ward and forward ready for action. When disturbed, they dart 

 away toward the bottom of the pond, carrying a supply of air for 

 respiration beneath their wings. As in the Corisidae, the body of 

 these insects with the air which they carry for respiration is much 

 lighter than water ; consequently, the moment they stop swimming, 

 they rise to the surface of the water if they do not cling to some 

 object to prevent it. Occasionally these insects will float on the 

 surface of the water with their dorsal aspect uppermost ; and, like the 



* Notongctidae, Notongcta: notes (vc5ro?), back; nectos (vrjKro^, swimming. 



