430 



MOSQUITOES 



lay their eggs singly (Fig. 194) while others lay them all at one 

 time in little boat-shaped rafts called egg-boats, the individual 

 eggs standing upright (Fig. 195). The fact that the eggs are a 

 little larger at the lower end makes the whole egg-boat slightly 

 concave, thus making it difficult to overturn. Most of the com- 

 mon mosquitoes of temperate climates lay their eggs on the 



open surface of water or at- 

 tach them to some partially 

 submerged object; a few 

 species lay eggs which sink. 

 Many species, however, 

 especially those of the far 

 north and of the tropics, lay 

 their eggs in dry places which 

 are likely subsequently to 

 be covered with water. In 

 T^ ,,^^ T^ c A 17 J • most mosquitoes of temper- 



liG. 194. t/ggsof Anopheles quadnmacu- . ^ 



latus on surface of water. X 13. (After ate climatCS the CggS hatch 



Howard.) • jj ^ £g^ days, or even within 



24 hours. In the species of the far north the eggs probably 

 never hatch until the following spring, being laid in depressions 

 on the ground which are usually riot immersed until the melting 

 of the winter snows. Such hibernating eggs are said not to hatch 

 unless they have been exposed to freezing temperatures. On the 

 other hand the mosquitoes 

 of dry hot countries lay 

 eggs which are highly re- 

 sistent to desiccation and 

 do not lose their vitality 

 during months of dryness. 

 Such species must almost 

 "live while the rain falls," 



and to win in the struggle against an unfavorable cUmate they 

 must be prepared to utilize the most transitory pools for the 

 completion of their aquatic immature stages. In such cases 

 the embryo within the egg shell develops to the hatching point, 

 so that it is ready to begin the larval existence almost with the 

 first drop of rain. Such mosquitoes further fortify their race 

 against the unkind environment by laying their eggs in a number 

 of small batches instead of in a single mass, as is the habit with 



Fig. 195. 



Egg boat of Culex floating on 

 water, x about 8. 



