CHAPTER XII. 

 FIELD WORK ON THE DIPTERA. 



This is such an immense order that there will be 

 attempted the study of only a few of the familiar dipters. 



These are the days of crusades against mosquitoes, 

 nevertheless there may still be found breeding-places 

 where may be seen the familiar wrigglers or mosquito 

 larvae. If you find such a breeding-place, bring in a cup- 

 ful of the water with the wrigglers in it. Divide it into 

 two parts and carefully pour on to the water surface in 

 one of the two tumblers enough kerosene to cover the 

 water surface with a thin film of oil. When you think 

 you have enough oil, watch the wrigglers to see what is 

 happening and to convince yourself of the effectiveness of 

 this treatment. What is the cause of the death of the 

 larvae? Do the dead larvas sink or float? What is the 

 reason for their position? Could their death be called 

 drowning ? 



With the reading glass examine the immature mos- 

 quitoes in the other glass. Are all the immature mosqui- 

 toes alike? Can you find any pupae ? What are the pupae 

 doing ? Can you discover what the larvae are eating ? Do 

 the larvae, when they come to the surface to breathe, rest 

 parallel with the surface of the water or at a decided 

 angle ? If you find parallel mosquitoes are they malarial 

 mosquitoes or not? If they hang at an angle, what 

 diseases may it be possible that they are carrying? Both 

 these forms of mosquitoes may at some future time be 



