18 AME R WAN MUSEUM GUIDE LEAFLETS 



gives an account of having repeatedly obtained certain mosquito larva* 



in large quantities, by thawing out ice which had formed in the leaves 



of the pitcher plant {Sarracenia)? When pools in which the wrigglers 



live dry out, the larva- usually perish in a short time. They are most 



likely to be found in small and undisturbed bodies of water, such as 



accumulate in little hollows between tufts of grass, in meadows, or in 



ditches where there is no perceptible Bow ( Fig. 1 1 1. Where there is any 



current in the water the larvae are easily swept away, and those that 



occur in moving water are always found along the edges of the stream, 



where they are out of reach of the current. Cat-tail swamps are said to 



he practically free from mosquito larva', probably because of the usual 



presence in them of small fish. Such places as neglected tin cans or 



broken bottles, lain barrels, cisterns and deep wells may be swarming 



with larva-. Dr. Howard mentions a case where the census 

 Number 



of the inhabitants of a rain barrel was taken. In one month 



it yielded .'5(i,.'!(i'» mosquito eggs, larva- and pupa;. 2 



The duration of the larval stage is usually from seven to fourteen days. 

 During this time the various parts of the adult insect are in process of 

 formation under the larval skin (Fig. 12). In older larvae the adult 

 eye, for instance, may be seen as a crescentic dark mass lying near the 

 larval eye. The legs and wings of the future " fly " may be seen form- 

 ing within the larval thorax. The formation of adult structures is ac- 

 companied by destructive changes in the strictly larval internal organs 

 and tissue. In due time, when this process has proceeded far enough, 

 a T-shaped split occurs in the back of the larval skin and through this 

 the insect emerges as a pupa. 



The Papa. 



The pupa which escapes from the larval skin forms the next stage in 

 the development of tin- insect (Figs. 13 and 14). It too is aquatic 



in habit and ordinarily leads a brief and comparatively quiet 

 of Pupa n '^ e - ^ '' <,(>s " ()t ' ( ' (>( '' Wh en at rest, it floats at the surface 



of the water, breathing through a pair of funueblike tubes. 

 It is, however, able to execute very rapid, though jerky, movements and 



'John B. Smith. X. .1. Slate Agr. Exp. Station. Report (in Mosquitoes, ]>. 

 :ilii. 1905. 



1 L. O. Howard. Mosquitoes, p. II. 



