THE BIONOMICS OF AUSTRALIAN TABANIDAE. 51 



apparent than in those bred under natural conditions. In a recent paper* it has been 

 stated that the wings show various gradations in colour from a total absence of 

 infuscation to a very pronounced shading, especially at the veins. A long series of 

 males and females bred out in this laboratory show these gradations to a marked 

 degree, not only in tlies reared from full-grown larvae captvired in natural surroundings, 

 but also in flies reared from the same batch of eggs. Variations in abdominal colora- 

 tion of both sexes, and especially in the females, is even more pronounced. In some 

 specimens there are evident spots at the apex of certain segments, in others the 

 abdomen is of uniform dark brown or uniform ochraceous tawny. In three wild 

 females captured in June in this district the colour of the abdomen is so light as to 

 lead the writers of the above-mentioned paper to refer them with some doubt to this 

 species. Recently, however, a similar form has been bred from a batch of eggs which 

 also produced individuals showing all the variations of wing and abdominal coloration. 

 It would appear that in this and other species too much attention has been paid in the 

 past to slight or even marked differences of this kind. WTien these variations in 

 colour are associated with abrasions of the abdomen and thorax, and especially of the 

 front, the possibilities of error in diagnosis are greatly increased unless a fairly long 

 series is available for comparison. 



In life the lower third and the lateral and posterior margin of the e^^es of the male 

 are claret-brown with emerald-green iridescence ; the upper two-thirds are drab grey 

 and composed of coarse facets. In the female the facets are small throughout and 

 the colour uniform drab grey with brown iridescence. 



Seasonal Occurrence. Throughout Australia, perhaps excepting the wet belts of the 

 North Queensland coast, of which I have little knowledge, there is a marked seasonal 

 occurrence of flies of this family, namely from about October to April. In the southern 

 regions, where there are regular winter rains and low winter temperatures, the 

 emergence of flies is probably regulated by temperature and not by rainfall ; but in 

 the north, where the temperature is more or less equable and the rainfall is, excepting 

 for moderate falls, confined to the summer months above mentioned, the condition of 

 the soil, whether dry or wet, is most certainly the regulating factor. Thus almost 

 invariably the march-fly season is either early or late, good or bad (from the collector's 

 point of view) according to whether the summer rain is early or late and normally 

 heavy, light or absent. 



The chief natural breeding-places in this district, and in most others with which 

 I am familiar, are in temporary accumulations of water, such as shallow swamps, 

 which disappear completely in the winter or dry season and after the full-grown larvae 

 have entered the soil in the vicinity of the water's edge, wherever that may be 

 at the time of their reaching maturity. As the soil dries these larvae are practicalh' 

 immobilised, and remain so until it again becomes thoroughly moistened. It 

 follows, then, that there can be no emergence of flies until after heavy rain has fallen. 



The truth of these statements has been demonstrated on many occasions, and 

 notably during the summer of 1919-20, when until 4th January the country was in 

 the grip of a severe drought, and there was an almost complete absence of Tabanids 

 in this district. Heavy rains for a short period in this month were followed by the 

 appearance of a moderate infestation of flies. (It may be stated here that the previous 

 season also was fine of unusually low rainfall, and therefore an unfavourable one for 

 fly breeding.) The January rainfall was not sufficiently heavy to raise the level of 

 the swamps to normal, and another long spell of dry weather intervened before the 

 banks in the vicinity of the normal high-water marks were thoroughly saturated. 

 About the middle of April abundant rains filled the swamps, and there followed a 

 marked increase in the number of flies in the district. Whether the flies were derived 

 from eggs laid in January 1920 or during the preceding wet season could not be 



* Ferguson & Hill, in the press (Proc. Linn. Soc. N.S. Wales). 

 416) d2 



