NO. I 



BLACK FLIES OF GUATEMALA — ^DALMAT 



335 



In considering the daytime resting places, cognizance was given to 

 past field experience of several of the laboratory workers who had 

 reported being bitten by black flies while they were climbing trees. 

 Thus, observation stations were established at different altitudes above 

 the ground level, where individuals remained for varying periods of 

 time to take notice of the activity of the flies. All observations were 

 made during the daylight hours. Records were kept of biting flies, as 

 well as of those that were actually resting. The results are given in 

 tables 21 and 22. 



Table 21. — Height range of principal anthropophilic species 



Expressed as number of biting flies captured per hour at difiFerent heights above 

 the ground. "Hours spent" represents a summation of the total hours during 

 which collections were made in trees at particular heights above the ground. 



Height range 



ochraceum 



metallicum 



Height 



in trees Hours 



(feet) spent 



Ground 172.7 



o- 10 3-7 



II- 20 91.3 



21- 30 61.8 



31- 40 108.7 



41-50 31.7 



51- 60 38.0 



61- 70 39-3 



71- 80 — 



81- 90 y.y 



91-100 4.7 



loi-iio 28.3 



111-120 4.0 



Number 

 4,961 

 277 

 3,970 



1,959 

 3.090 



452 

 129 

 676 



42 



69 



17 



3 



Num- 

 ber/ 

 hour 



29 



75 

 43 

 22 

 28 

 14 

 34 

 17 



5 



15 



I 



I 



Number 

 7,453 

 133 

 5,540 

 3,137 

 4,290 



903 



756 



1,042 



108 

 124 



551 

 100 



Num- 

 ber/ 

 hour 



43 



36 

 61 



51 



39 

 28 



19 



27 



14 

 26 



19 



25 



callidum 



Num- 

 ber 



380 

 19 



215 



218 



201 

 38 

 51 

 62 



Num- 

 ber/ 

 hour 



5 I 



o 



28 I 



3 I 



It will be noted in table 21 that Simulium ochraceum, metallicum, 

 and callidum will all bite man from the ground level up to at least 

 120 feet. 5". ochraceum appears to prefer altitudes from the ground 

 level to about 70 feet, above which few were found to feed. On the 

 other hand, metallicum and callidum seemed to bite almost indiscrimi- 

 nately from the ground level to the highest established stations, with 

 only a slight preference shown for stations closer to the surface of 

 the ground. From table 22 it can be seen that all three species rest in 

 the trees, at times for long periods. It was difficult to secure abundant 

 and accurate information relative to resting periods, since flies that 

 were close enough to be observed would usually take to wing owing to 

 unavoidable movements of the observer. 



