I 12 



ELEMENTARY ENTOMOLOGY 



leap for some unwary midge or other small insect. They usually 

 occur together in some numbers, and some kinds have been seen 

 on the ocean hundreds of miles from land. 



All of the aquatic bugs are predacious upon other insects or upon 

 small aquatic animals or fish, and may therefore be either beneficial 

 or injurious, according to the nature of the food. 



FIG. 148. The wheel-bug (Prionidus cristatns Linn.), eggs, nymphs, and adults 

 (After Glover, United States Department of Agriculture) 



The predacious bugs. Several terrestrial families are predacious 

 and may be conveniently considered together. The assassin-bugs 

 (Rcthwiidae) are well named in this respect. They feed on soft- 

 bodied insects, but unfortunately are not discriminating in their 

 choice, so that frequently beneficial insects are destroyed in large 

 numbers. They are more common in the South, where one of the 

 largest species is known as the wheel-bug (Arilus cristatus] from 

 the large hump, like a cogwheel, on the back. In the North are 

 several species, commonly found around houses, one of which is 



