16 BACK-SWIMMERS. 
very common, but they prefer shallow lakes to deeper ones. Here 
they float on the surface of the water, back downward, with 
the tip of their abdomen projecting sufficiently to admit air into 
the space below their wings. Their oar-shaped hind legs are 
stretched outward and forward, ready for action. When dis- 
turbed they dive, carrying a bubble of air beneath their wings. 
Although decidedly aquatic, they are also attracted to the elec- 
tric light, and are not such harmless beings as the water-boat- 
men. Like these they can leap from the water to take flight, 
but if water plants project over the surface of the water they 
utilize these to start from. It is very interesting to watch a 
Fic. 10.—Notonecta undulata Say. Upperand lower side, beak and leg. Original. 
pond which is drying up, and to observe the immense number 
of insects, not even suspected before, which are now forced to 
leave in search of new homes; and how they leave the water by 
utilizing all sorts of objects upon which to rest before unfolding 
their wings. Many project themselves, like flying-fishes, out of 
the water, instantly unflolding and using their wings. 
These curious back-swimmers are no doubt decidedly in- 
jurious, as they kill large numbers of small fish; from which 
they suck the blood. This can be seen by keeping fish and bugs 
together in an aquarium; before long the latter will be the only 
living inhabitants. 
