34 ANIMAL BIOLOGY 



the light is reflected from the bubbles. Backswimmers 

 live by sucking out the blood of small animals of various 

 kinds, and they may attack insects larger than themselves. 

 They are readily kept in aquaria, but too many of them 

 must not be put together as they will sometimes attack 

 and devour their own kind. Like many other aquatic 

 Hemiptera, backswimmers are strongly attracted by light, 

 and may be made to follow a light about in any direction. 

 Similar in habits to the backswimmers are the water boat- 

 men which also get their supply of air by placing the tip 

 of the abdomen at the surface of the water. 



FIG. 27. The periodical cicada. Upper figure, adult female; 6, beak; 

 o, ovipositor. Lower figure, young larva enlarged. (After Riley.) 



While most of the aquatic Hemiptera live within the 

 water, the water striders of pond skaters are found upon 

 the surface, being supported by the surface film which 

 they are not heavy enough to break through. Insects 

 which fall upon the surface are quickly attacked by 

 these watchful rovers. 



In the sub-order Homoptera the fore wings when present 

 are membranous throughout. One of the largest of this 

 group is the harvest fly or cicada, whose prolonged and 

 uniform note is often heard during the hot days of late 

 summer. Another member of the same genus is the seven- 



