218 The Philippine Journal of Science ms 



Tabanus striatus of both sexes at all hours of the day and far 

 into the night. During the cooler part of the day the flies 

 assemble on the trunk and main branches, but when it is sunny 

 the upper limbs and leaves are resorted to ; on windy days they 

 may be found at all hours perched on the side of the trunk of 

 the tree shielded from the wind. During their greatest preva- 

 lence they are found in large numbers indoors in the lightest 

 portions of the room, usually perched on the windows. 



The flies obtained for this biological study were collected 

 from rain trees in the vicinity of the laboratory. These when 

 gathered were identified and turned loose in the large breeding 

 cage where two carabaos furnished the food required for further 

 development. The daily supply of flies varied from 25 to 300 

 according to their prevalence and the skill of the Filipino 

 collectors. Insect nets were used for trapping. 



In 1912 the first appearance in this locality of horseflies in 

 appreciable numbers was on August 15. From that time ta- 

 banids were collected daily at the rate of 25. August 15 to 

 September 4 males predominated in the proportion of 2 or 3 to 1 

 female; and shortly afterward the female count increased to 

 the proportion of 1 male to 1.7 female. There was a constant 

 . preponderance of females to the extent of 3 to 1 in October and 

 4 or 5 to 1 in December. 



Beginning September 4, there was observed the first appear- 

 ance of mammalian blood in flies collected from rain trees. The 

 source of this blood, which showed itself in the dejecta and dis- 

 sected stomachs of the females, was presumably a herd of 50 

 cattle which had been grazing on land along the lane of trees 

 which harbored the flies. Although the cattle were present for 

 eight days previously, blood was not taken until September 4. 

 From September 4 to September 6 every lot of females collected 

 was found to contain a preponderant number of individuals con- 

 taining blood. 



The first occurrence of oviposition was observed in a female 

 collected in a lot of flies from this locality. It was removed 

 from a tree September 10, and found laying eggs the following 

 day, September 11. These eggs proved fertile, and were sub- 

 jects of the life-history study described in this paper. 



SUMMARY 



1. The eggs of Tabanus striatus Fabricus have been found in 

 masses of from 270 to 425, laid mainly on particles of wood. 



