FLIES 217 



on flowers she will also pierce the involucral bracts in order to get at the 

 honey. When the female is fully fed her voice drops in pitch from F to 

 D. She is a voracious feeder and will ingest 1.2 miUigrams of blood in 

 a single meal although her own weight is only 1.4 miUigrams. Small 

 wonder that her voice becomes a trifle mellow. 



Unlike the male, the female house-gnat survives the winter by 

 hibernating in cellars, cool outhouses, dairies and cricket pavilions and 

 living upon her own fat-body which is a reservoir of food. If she mates 

 in the autumn she can store the sperm in her body and fertihse her 

 eggs in the spring. 



In Part II it was shown that different species of bird fleas are 

 "zoned" according to the nesting habits of the host. Different species 

 of mosquitoes also frequent fairly well defined elevations — a fact which 

 is most noticeable when they swarm. Traps baited with living birds 

 reveal that different genera and species are caught near the ground, in 

 the lower and middle branches, and near the tops of trees. In nature 

 there is probably a closer link with definite species of bird host than has 

 hitherto been realised. 



As carriers of disease female mosquitoes have no equal. Malaria, 

 yellow fever, dengue and filariasis are among the maladies transmitted to 

 man in the tropics. In Britain they transmit malaria and fowl-pox to 

 birds and probably also filaria. They themselves have many enemies. 

 Water-beetles, dragon-fly larvae, various small fish and newts feed 

 voraciously on the immature stages. In the course of nine nights one 

 newt ( Triton) ate no less than 985 gnat larvae. Bats and birds, especially 

 swallows and swifts, feed eagerly on the adults. Apart from one midge 

 which sucks blood directly from gorged female mosquitoes instead of 

 from the body of a mammahan host, they are free of insect parasites. 

 This is remarkable when we consider the vast number of species which 

 attack butterflies, moths, beetles and wasps, and so forth. 



Naturally the best known parasite of the house-gnat is the malarial 

 Protozoan, Plasmodium relictum, and its alHes. Susceptibility to 

 malaria appears to be hereditary in C. pipiens, and some strains are 

 completely resistant. The egg production of infected females is greatly 

 reduced and in this manner, as well as in a variety of other ways, it has 

 a deleterious effect on the host. There are also numerous other fatal 

 and harmful parasites of both larva and adult, ranging from Protozoa 

 and Fungi to scarlet hydrachnid mites, so it must be admitted that 

 mosquitoes themselves are not without their troubles. 



