VIl] BIOLOGY OF ADULT MOSQUITO 67 



its abdomen and floats almost horizontally on the surface of 

 the water. The thoracic region then splits longitudinally and 

 the adult mosquito gradually draws itself out of the skin and 

 after a few minutes is able to fly away. 



Biology of the Adult Mosquito. 



Food-habits. Although the females of a large number of 

 species of mosquitoes habitually feed on blood, the habit is 

 by no means universal throughout the family, as practically 

 all the males and a considerable number of the females feed 

 on various plant juices. Some species, e.g. Stegomyia fasciata, 

 attack man much more readily than others. The majority 

 of the Culicinae seem to be mainly parasitic on birds. 



Mosquitoes are very susceptible to heat and cold, for during 

 the winter they never bite except on occasional warm days. 

 The reaction to heat is so striking that this is probably one 

 of the main reasons of their being attracted towards warm- 

 blooded animals and other warm objects. Hewlett has shewn 

 that hungry female mosquitoes [Anopheles and Culex) will bite 

 viciously at a test-tube of boiling water, or even of hot copper 

 sulphate solution. In the latter case the insects could be 

 observed to thrust their proboscides into the crust of copper 

 sulphate that had crystallized on the outside of the tube. It is 

 possible that the blood-sucking habit may have been derived 

 from what was originally a simple thermotropism (attraction 

 by heat). A large number of mosquitoes feed only at night, 

 but Stegomyia fasciata and most of the northern species, and 

 also those inhabiting jungle, feed during the day-time. 



The method of feeding. When a female mosquito commences 

 to feed, the tip of the labrum is placed against the surface, 

 and then the sharp maxilla; and mandibles are thrust into the 

 skin. The labrum is then forced into the wound and thus 

 the whole six stylets of the proboscis enter the skin, being 

 guided by the labium. The latter is doubled back as the 

 mouth-parts enter deeper into the host. 



The subsequent processes can only be conjectured from 

 experiments on mosquitoes under artificial conditions, but are 

 probably as follows. 



5—2 



