THE LENGTH OF THE FLY^S LIFE 87 



even in the warmest weather for sixteen weeks. Yet 

 very hot and very dry weather certainly does kill off a 

 large number of flies. But then a drought will cause the 

 rapid development of the eggs, larva?, and nymphs, and 

 will cause the hibernating females to lay more eggs. The 

 length of life of individual flying insects is very difficult to 

 determine exactly, because captivity must produce great 

 modification in their lives ; it seems impossible to measure 

 the lives of these insects under natural conditions. 



There are certain questions concerning the life- 

 history of these insects which require elucidation. It 

 is most important that the normal length of life of both 

 male and female flies should be discovered. It is also 

 most important that the time of the occurrence of 

 sexual maturity and mating should be learned. Much 

 depends upon these points. Once the exact details of 

 the natural lives of flies are fully known, the problem 

 of fly-reduction should be much simplified. Research 

 is required; but research is a costly thing, requiring 

 much patience and persistent attention to little 

 observations and details. Information concerning flies. 

 however, would well repay the cost of research ; for 

 the result would be improved health. Hewitt states 

 that flies become sexually mature ten to fourteen days 

 after they emerge from the pupa-case ; and that four 

 days after mating the female lays her eggs. Griffith, 

 another observer, found that flics lay their eggs when 

 the females are ten days old. But if the length of the 

 summer life of the fly is only three weeks it gives but 

 a short period for sexual maturity, although Griffith 

 states that flies will lay fresh batches of eggs every ten 

 days. In all probability it will be discovered that flies 

 live much longer than is generally believed and that 

 cage experiments are misleading. 



