14 



Larva.— The egg hatches into the larva ("wiggle-tail") (fig. 6), 

 which can be distinguished readily from the larva of Culex pipiens 



(fig. 7), its most common messmate, by 

 the color and proportions of the breath- 

 ing siphon (air tube). In the S. calopus 

 the respiratory siphon is black and 

 somewhat barrel-shaped, with its great- 

 est transverse diameter equal to about 

 one-half of the length; whereas in Culex 

 pipiens the air tube is brown, longer, 

 more slender, and with the greatest 

 transverse diameter less than one-third 

 of the length of the tube. The larva,, 

 though it lives in the water, is strictly 

 an air breather and must come to the 



Flo. 6.— Larva of Stegomyia calopus (after 

 Howard, 1901). 



surface for air. It thrusts its breath- 

 ing tube up into the surface film and 

 remains suspended head down, at an 

 angle somewhat less than 45°, for a 

 variable time. A film of oil on the sur- 

 face of the water is sufficient to obstruct • 

 the air tube, and thus cause the death 

 of the larva by suffocation. The larva 

 is very timid, so that a very slight jar 

 or a sudden shadow will cause it to 

 move rapidly to the bottom of the 

 container where, indeed, it may very 

 commonly be observed to feed. 



The duration of the larval stage is influenced by food supply and 

 temperature. With an abundant supply of food and under favorable 



-Larva of Culex pungens (after 

 Howard, 1901). 



