39 



in hornets' nests, has only a slight colour resemblance to its host. 

 Still, there are many remarkable mimics of aculeate Hymenoptera 

 amongst Diptera. To take another instance, in several of the 

 Syrphidcc there is a dark blotch in the middle of the wings usually 

 correlated with a pale area at the base of the abdomen. When the 

 fly is at rest this dark blotch does not cover the pale area as might 

 be supposed, but as a rule comes into line with, and spreads out on 

 both sides of, the darkened abdominal segments immediately below 

 the pale area above referred to. This arrangement of light and 

 shade helps to break up the outline of the insect when settled and 

 motionless, and fits in admirably with Mr. Thayer's theories of 

 colour protection 5* but, if this is so, how is it that we meet with 

 so few examples compared with the vast number of Diptera that 

 employ no such device ? Another subject that has attracted attention 

 lately is that of the predacious Diptera,! and there are many points 

 of interest in this connection : The different kinds of prey affected 

 by various Diptera, some keeping more or less closely to one kind, 

 others with more catholic tastes ; the manner in which the victims 

 are overcome; if, for example, some of the larger Asilidcz poison 

 their prey ; the extraordinary mating habits of certain EmpidcE^ the 

 male obtaining and giving to the female living prey, presumably to 

 distract her attention from himself as a possible victim instead of 

 husband. Then, too, there is the subject of the fertilization of flowers 

 by Diptera, + in which the flies appear quite able to exercise a choice 

 as to colour, and to some extent effect a modification of flower- 

 structure. Lastly, one can approach the study of Diptera from the 

 side of Economic Entomology. I am not personally acquainted with 

 this branch of science, so must pass it over briefly. Diptera are 

 of course of great importance in economic entomology, and if we 

 consider those insects that directly attack man the order is more 

 important than any other. The mosquitoes that are associated with 

 malaria and yellow-fever, and the tse-tse fly that carries the infection 

 of sleeping-sickness, are of course pre-eminent, but in our own 

 country the house-fly has been accused of being an active agent in 

 spreading disease. The various species of flies that torment live 

 stock, the Hessian fly and many others that infest crops, have all to 

 be taken into account by the student of agricultural zoology. This 

 is but the briefest summary of the connection of flies with economics, 

 but the subject is an important one, and has attracted a vast deal of 

 attention recently ; for it is only a decade ago that Dr. Sharp, writing 

 in the " Cambridge Natural History,"§ said : " There is good reason 

 for supposing that mosquitoes may act as disseminators of disease, 

 but there is no certain knowledge on the subject"; whereas, in 

 August of this year, Mr. A. E. Shipley, in his address to the 



* " Ent. Soc. Trans.," 1903, pt. iv, 



t Ibid., 1906, p. 323. 



X Ibid., 1896, p. 117. 



§ " Insects," pt. ii, p. 468. 



