320 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I25 



depth, and once feeding, the fly will not remove its mouthparts or fly- 

 away, even when touched by the fingers, stroked by another object, 

 or covered by a collecting tube. .9. metallicum and callidum, on the 

 other hand, hover about the subject and may land momentarily several 

 times before finding a suitable spot. Once landed, these species move 

 about on the skin before inserting the mouthparts. While feeding, 

 they often move the legs and body. Although these flies will not leave 

 the host when the part they are biting is moving slowly, they will 

 stop feeding and fly away should they be touched, stroked, or crossed 

 by a shadow of a collecting tube. The behavior pattern of ochraceum 

 would indicate that this species might be more efficient in transmitting 

 the infective stages to man since its feeding is not easily interrupted, 

 thereby permitting sufficient time for migration of infective stages to 

 the mouthparts. On the other hand, because of its opportunity for 

 noninterrupted blood meals, this species is likely to pick up large 

 numbers of microfilariae, the presence of which might cause the death 

 of the flies. 



Effect of Environment on Feeding Habits 



In an attempt to learn the effect of some of the environmental factors 

 on the feeding habits of the three anthropophilic species, a large series 

 of experiments was carried out. On 95 days, from the hours of 

 6 to 6 130 a.m. until 5 130 p.m., subjects were exposed in the field to the 

 bites of the flies, each subject being accompanied by three observers. 

 In some of the experiments the subject rotated with the movement of 

 the sun, in others he kept stationary. The following factors were 

 notated every 10 minutes: Time, temperature, reflected light (from 

 chest and back), relative humidity (every 30 minutes), general 

 weather conditions (clouds, clarity of sun, etc.), the species of fly 

 biting, part of body attacked by fly, and whether the biting fly was in 

 the sun or shade. Relative humidity data were taken during 69 

 experiments only. 



Relation of time of day to biting habits. — In table 16 a summary of 

 the relation of time of day to the biting habits of vS". ochraceum, 

 metallicum, and callidum has been given. S. ochraceum, appears to 

 bite from about 7 a.m. until 4 p.m., few feeding before or after these 

 extremes. The most active feeding period is from 8 a.m. to 10:00 a.m. 

 The effect of the time of day seems to be the same for flies feeding on 

 shaded regions or those exposed to the sun, although less actual feed- 

 ing takes place in the sun. S. metallicum starts feeding in the morning 

 at about the same time as ochraceum, preferring the hours of 8-10 a.m., 

 but it continues to feed in good numbers until 5 :30 p.m. S. callidum 

 differs from both ochraceum and metallicum in that it prefers to bite 



