THEIR RELATION TO MAN 209 



from that surface of the egg that rests upon the water, 

 and the minute wriggler slides at once into its natural 

 element. This "wriggler" is so named from its peculiar 

 jerky mode of progression. It has, attached to its 

 mouth, a pair of very dense brushes of fine hair, and 

 these brushes are kept in constant motion, combing 

 from the water and into the mouth the minute organisms 

 upon which the creature subsists. At the other end of 

 the body is a cylindrical tube of moderate length, at the 

 tip of which are the spiracles or openings to the breath- 

 ing tubes, by means of which air is secured from above 

 the surface of the water; for the larva although strictly 

 aquatic as to food and other habits, is yet dependent 

 for its supply of oxygen upon the outer air, and must 

 come to the surface at short intervals to breathe. Indeed 

 the favorite position of this larva is to hang head down 

 in the water, the tip of the tube at the surface, the 

 mouth brushes hard at work securing food. This pecu- 

 liarity of the insect gives us a certain advantage in our 

 efforts to control their increase, for a film of oil on the 

 surface of the water in which they live will prove rapidly 

 fatal, the oil entering into the body through the spiracle 

 when the insect attempts to get air. 



In from five to seven days during the summer, the 

 larvae are full grown and change to pupae in which the 

 outline of the future mosquito can be made out hunched 

 into a comma-shaped mass. This pupa also gets its air 

 supply from above the surface, through two small, 

 trumpet-shaped tubes on the thorax, so that it is also 

 fatally affected by oil. It is active in this stage when 

 disturbed, and moves about rapidly but erratically, by 

 means of two paddle-like structures at the end of the 

 abdomen. When it becomes quiet it rises automatically 

 to the surface, and there rests until ready to assume the 

 adult stage, which is in from one to three days in summer. 

 14 



