146 INSECT LIFE. 



stream at any season of the year and you will find 

 nymphs and larvae of various kinds clinging to their 

 lower surface. If before lifting the stones you will 

 place a net in the stream just below them, other in- 

 sects that live beneath the stones will be swept into 

 it by the current. 



A great variety of insects live in such places, the 

 kinds differing in different localities. But there are 

 certain families that are almost sure to be represented 

 in any rapidly flowing stream ; they are the stone- 

 flies, the May-flies, and the caddice-worms. These 

 and a few others are described below. 



Most of these insects are not easily kept in aquaria 

 without running water. But if you can place an aqua- 

 rium under a faucet, and keep the water from over- 

 flowing by the use of a constant-level siphon (see 

 page 331), you may be able to preserve living speci- 

 mens for study. 



If you are unable to do this, study the insects as 

 well as you can in the field, and bring back speci- 

 mens for your collection and for a study of their 

 structure. 



The Nymphs of Stone-flies {Field and School 

 Work). — In most localities the insects that occur in 

 greatest numbers on the lower side of stones in the 

 beds of streams are the nymphs of stone-flies, and it 

 was probably this fact that suggested their common 

 name. Usually the first stone lifted from a riff will 

 be found to bear several of these insects clinging to 

 it, or scurrying over its surface in their efforts to 

 escape. When at rest the very flat body is closely 

 applied to the stone, while the legs, antennae, and 

 caudal setae radiate from it on the surface of tha 



