240 



THE RISE Or ANIMAL LIFE 



Fig. 11-37. The praying mantis (Sfagmomanf/s Carolina) 

 has its anterior legs modified into grasping append- 

 ages. It gets its name because of its manner of pos- 

 ture while waiting for some unwary insect to ap- 

 proach within striking distance. It is one of the larger 

 insects, reaching a length of 4 inches in some of the 

 larger specimens. 



sect (Fig. 11-38). The cicada has special 

 organs to make its shrill song (Fig. 11-39). 



The chief modification in the abdominal 

 region is the ovipositors of the female. 

 These have been described for the bee and 

 the grasshopper. In some insects, however, 

 the ovipositor is developed in a most ex- 

 traordinary fashion. Thus in the Ichneumon 

 fly, it is several times as long as the body 

 and can drill a hole in wood an inch or more 

 deep. Since this insect lays its eggs in the 

 body of the larval wood beetle, such an ap- 

 paratus is essential. 



The over-all color of insects varies as 

 much as it does in birds, from the brilliant 

 iridescent green Japanese beetle and highly 

 colored butterflies to the inconspicuous drab 

 color of the housefly and the camouflaged 

 walking stick. The colors are either in the 



exoskeleton or they are produced by differ- 

 ential interference of light impinging on 

 regular minute depressions and elevations 

 in the cuticula. Some insects resemble other 

 insects or parts of their environment. One 

 species of fly, for example, resembles and 

 even acts like a bee, thereby taking advan- 

 tage of the protection of the bee's sting, 

 even though it has none itself. This is called 

 mimicry. The mimic takes advantage of the 

 weapon carried by other insects, simply by 

 resembling it in both coloration and in ac- 

 tion, and is thus able to discourage its nor- 

 mal enemies. Other insects, such as the 

 walking stick, resemble the twigs and leaves 

 of the bush upon which they rest to such 

 a great extent that they are not easily seen 

 and when discovered even become stiff like 

 a leaf petiole. 



There are numerous modifications in the 

 respiratory systems. Although most of the 

 insects breathe air, some, such as caddis fly 

 larvae, receive their oxygen by means of 

 thin gills and can get along perfectly well 

 under water. These gflls are not, however, 

 in any way homologous to the gills of the 

 Crustacea. It is clear that the insects be- 

 came air-breathing arthropods and that 

 only a few have secondarily gone back into 

 the water during their larval Hfe. It is also 

 interesting to note that they have taken 

 only to fresh water and not to salt water. 

 This would be expected, since the osmotic 

 pressure of the tissues of insects is quite 

 different from that of the sea today, al- 

 though it may have been the same when the 

 insects, or their progenitors, left their ma- 

 rine life long ago. It must be mentioned, 

 however, that some vertebrates, such as tur- 

 tles, seals, and whales were able to over- 

 come this difficulty and returned to the sea. 

 Finally, some insect larvae can survive in 

 the mud at the bottom of bodies of water 

 where oxygen is absent. They receive their 

 oxygen by breaking down organic matter 

 there, just as many anaerobic bacteria ( bac- 

 teria that live without free oxygen) do. 



The digestive systems of insects vary con- 



