THE MARGUERITE FLY. 29 



or hopping flight, very seldom flying more than a few feet at a time. The 

 periods between flights may be quite long, unless the flies are disturbed, 

 and great portions of these periods may be spent at rest in one place. 

 The males are, as a rule, more active than the females, the latter being 

 also more tame. 



Their activity and degree of tameness vary, also, with the time of day, 

 with the degree of sunhght and with the temperature. They are com- 

 paratively tame in the early forenoon, late afternoon and on cloudy days. 

 Inactivity and drowsiness, as might be expected, are strongly marked at 

 lower temperatures. Both males and females are tame while mating and 

 after, although the female remains thus for a much longer period. 



While inactive in darkness they at once become active when brought into 

 bright artificial light. They have been observed to mate in such light, 

 and as will be seen later, will even oviposit. 



Both sexes are strongly negatively geotropic, seeking, as a rule, the 

 highest point of an object or vessel in which they are confined, a trait 

 which was found very useful, and of which full advantage was taken by 

 the writer during the investigations. 



Mating. 



Newly emerged flies kept in confinement in the laboratory, to determine 

 how soon after emergence mating begins, yielded rather widely variable 

 results; that is, there was a wide variation in the length of time elapsing 

 between emergence and coupling for different individuals. While most 

 of the individuals which were confined together for this purpose were 

 of about the same age, some were of different ages, the age varying with 

 the one or the other sex. These periods between emergence and mating 

 ranged from approximately six to approximately forty hours, and were 

 more or less scattered between the two extremes. Under natural condi- 

 tions, with the flies free and at large on plants, the results would probably 

 be modified. For instance, it is doubtful if under natural and normal 

 conditions, with both sexes in abundance, individuals would abstain from 

 mating for so long a period after emergence as did some in confinement in 

 the laboratory. On the other hand, the fact that some united about six 

 hours after emergence, would seem to indicate that in some instances, at 

 least, mating takes place very shortly after emergence. 



The length of time that couples remain united also varies. In one 

 instance a couple remained attached for three and one-half hours, in 

 another, two and three-quarters hours, and in another two hours. The 

 more usual period, however, seems to be from one-half to one hour. As 

 compared with the same in other Diptera or flies^ this is rather short. 

 The "northern cherry fruit flies," for instance, according to J. F. Illing- 

 worth, may remain coupled for eighteen and one-half hours. (Bull. No. 

 325, Cornell University, 1912.) 



The male mounts the female, as a rule, when the female is at rest, by 

 grasping her with his anterior legs and pulling himself up on her back. 



