124 INSECT LIFE. 



rowing they fall upward. This load is a film of 

 air, which can be seen shining through their wings 

 like burnished silver. Knowing this, we can under- 

 stand how the back-swimmers can remain so long 

 at the bottom of the aquarium without strangling. 

 Occasionally these insects will float on the surface of 

 the water with the back uppermost ; when in this 

 position they can leap into the air from the water 

 and take flight. It is necessary, therefore, to keep 

 aquaria containing them covered, in order to prevent 

 their escape. 



Let us study these creatures more closely : 



1. Kill two or three specimens by putting them 

 into a cyanide bottle. In handling back-swimmers 

 care must be taken or they will inflict painful stings 

 with their sharp and powerful beaks. 



2. When those in the killing bottle are dead,, pin 

 them so that they can be handled conveniently. Put 

 the pin through the three-cornered piece on the mid- 

 dle of the back (the scutellum), so as not to fasten 

 the wings down. 



3. Hold the insect back downward and note the 

 boat-shaped form of the body, the middle of the back 

 representing the keel. 



4. Study the head and observe the following 

 parts : The eyes — these are very large, and each has 

 two large scallops in the outer (lateral) side. The 

 antennas — these are often so concealed that it is diffi- 

 cult to see them ; each is situated just behind that 

 scallop of the eye of the same side which is nearest 

 the mouth. The beak — this projects backward be- 

 tween the legs. What insects already studied have 

 similar mouth-parts ? To what order do they belong ? 



