The Wonderful Ways of Insects and Spiders [ 267 



weather lasts, generations follow each other from within two 

 weeks to a month. 



The arrival of cold weather destroys the adult flies, eggs, and 

 larvae. The pupae in their protective shells survive, remaining 

 inactive during the winter. With the onset of warm weather they 

 quickly complete their development, and the same process begins 

 all over again. The average life of an adult is from two to three 

 weeks; some live considerably longer. 



The Fly's Cleaning Routine: If you have ever watched a fly clean- 

 ing itself, you must have wondered at its reputation for filthiness. 

 Its grooming is remarkably thorough. First it rubs its front feet 

 together briskly so that the hairs on one leg act as a brush for the 

 other leg; then the fly nibbles at the front feet with the rasping 

 disk it has in lieu of teeth. 



Next the creature gives its whole head an energetic scrubbing 

 with its clean front feet. It pulls forward its middle pair of legs, 

 one at a time, and brushes and nibbles them. Finally its hind feet 

 are used to clean each other and to brush its wings and most of 

 its body. 



All this careful grooming is deceptive, however, as far as pro- 

 tecting our health is concerned. Flies breed in manure and the 

 odors of fermented or decayed plants and animals have a special 

 attraction for them. Harmful germs cling to their feet and are 

 deposited in food on which they may alight. Typhoid fever and 

 amebic dysentery are among the many diseases they are known to 

 spread. It is true that many kinds of flies render important service 

 as scavengers and exterminators of other objectionable insects; 

 but credit is given them grudgingly, if it is given at all, because 

 their relatives are so unpopular. 



The Fly's Wing Structure: Flies differ from most other adult 

 insects in having a single pair of wings x mstead of two pairs. 

 (Dragonflies, mayflies and others with four wings are not really 

 flies.) Nevertheless they seem able to keep flying indefinitely, as 

 you will notice when you chase one with a swatter. Hind wings 

 are replaced by short stalks, or knobs, which are important in 

 balancing them as they fly. 



