322 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I25 



than at lower humidities, its optimum appearing to be between 8i and 

 90 percent ; there is marked reduction in biting activity above 90 ; at 

 higher humidities, especially in its optimum range, this species defi- 



Table 17. — Relation of air temperature to biting habits of adult Simuliidae 



Expressed as number of flies biting per observation period 



(Flies collected while feeding on human subjects who were exposed to bites on 

 95 days from 6 :30 a.m. until 5 :30 p.m. Air temperature was recorded every 10 

 minutes. Sun or shade readings indicate that the flies were biting on a part of the 

 body that was either exposed to the sun or shade.) 



Number of Number of flies biting per observation period 



observation , -^^ ; > 



Tempera- periods ochraceum metallicum callidum 



ture , ^ » , -^ N I * \ I ^ > 



(o C.) Sun Shade Sun Shade Sun Shade Sun Shade 



<i3 19 22 0.9 2.0 o 0.3 0.05 0.6 



13 II 26 0.6 2.2 o 0.7 0.09 0.5 



14 55 58 0.6 3.6 o 0.9 0.02 0.9 



15 72 82 2.3 3.8 0.3 0.9 0.09 0.6 



16 107 157 1.6 2.6 0.3 0.9 0.09 0.4 



17 142 283 2.2 3.0 0.2 I.I 0.06 0.9 



18 268 419 1.7 4.7 0.3 1.3 0.08 0.4 



19 251 482 2.3 4.8 0.7 I.I 0.2 0.2 



20 360 700 2.0 4.2 0.7 1.6 o.i 0.2 



21 304 533 2.4 2.5 0.8 1.7 0.03 0.2 



22 318 671 3.1 4.6 1.6 2.3 0.07 0.2 



23 257 436 3.4 5-9 i-o 2.0 0.03 0.1 



24 215 345 5-7 7-1 1-9 2.0 0.07 0.3 



25 259 266 5.3 5.9 1.4 2.8 0.03 0.1 



26 222 227 6.7 5.5 1.8 2.3 0.03 0.1 



27 139 150 6.9 7.1 2.5 3.8 0.02 0.1 



28 117 124 6.2 6.8 2.2 2.0 o.oi 0.1 



29 41 41 7-6 5-7 2.1 1.5 0.04 o 



30 50 50 7.1 10.6 1.9 1.5 0.02 0.03 



31 40 40 4.1 5.2 1.5 1.9 o 0.05 



32 41 41 7.8 7.6 2.0 1.3 o 0.02 



3Z 31 31 5-6 7-5 1-2 1.9 o 



34 28 28 16.7 17.6 0.6 0.4 o 0.03 



35 48 48 15.6 19.4 1.2 0.6 o o 



36 19 19 7.9 2.9 1.2 0.7 o 



37 15 IS 3-0 2.3 0.7 0.9 o 



38 12 12 3.1 1.3 2.1 0.5 o o 



39 7 7 50 i.o 1.8 0.5 o o 



40 13 13 2.6 1.6 1.2 2.2 o 



>40 22 22 2.0 1.6 I.I 1.3 o o 



nitely prefers biting in the sun; from 41-80, it prefers feeding on 

 shaded parts of the subject, except between 51 and 60, when the feed- 

 ing is almost indiscriminate on regions exposed to the sun or shade ; 

 in the shade, fewer flies bite in relative humidities within the optimum 



