16 BULLETIN 1328, U. S. DEPARTMENT OF AGRICULTURE 



It is noticed that the bees did not respond to the cloudiness at 

 2.30 p. m. ; but when the sky darkened at 2.45 p. m. the curve rep- 

 resenting incoming bees immediately began its rapid ascent and the 

 outgoing bees showed a decrease, the divergence of the two curves 

 continuing at an equal rate until 3.15 p. m., when the greatest number 

 of returning bees had entered the hive. The climax of the threaten- 

 ing storm was just previous to 3.30 p. m., when 'the curve of outgoing 

 bees reached its lowest point, and all but 13 of the bees in the field 

 had entered the hive. At this point the surprising fact is revealed 

 by this day's record that, although the storm was so severe as momen- 

 tarily to send all the field bees back to the hive, the impulse of the 

 bees to go to the field while the secretion was good was so strong that 

 in the half hour in which the climax of the threatening storm 

 occurred as many as 50 to 75 per cent of the bees, which were going 

 out under optimum conditions for this day, were still leaving the 

 hive. The quick response of the bees, this time to the gradual but 

 rapidly improving conditions of the weather, is seen from 3.30 to 

 4.15 p. m., when normal activity was resumed. It is interesting to 

 speculate as to just what feature of the storm contributed most to 

 this behavior in the flight of the colony. Was it drop in tempera- 

 ture, variation in light or atmospheric pressure, difference in humid- 

 ity, intensity of the wind, or general change in the electrical con- 

 ditions of the atmosphere ? Unfortunately, not all of these questions 

 can be answered definitely as yet. 



Of all these factors, temperature and light varied most. If tem- 

 perature had been the chief cause, the flight might have been ex- 

 pected to remain low after the storm, since the temperature remained 

 low for the remainder of the afternoon. The response to the change 

 in light, both its increase and its decrease in intensity, can be so 

 closely correlated with the flight activity that this may be safely 

 considered the chief cause of the variation. 



Comparing this day with May 13 (see Table 1), when the number 

 of field bees was perhaps slightly less and on which there were 58,887 

 returns, we find that there were only 54,528 on May 15, which shows 

 that the threatening storm of the latter day reduced the total flights 

 by at least 7.40 per cent. On the assumption that the nectar condi- 

 tions on these two days were identical, this represents a loss of 69.58 

 grams, due to this clouding over. Actually 90 grams less nectar 

 was gathered, which would indicate that there was little or no dif- 

 ference in the nectar conditions on these two days. 



Comparing May 15 with May 16, which was bright and sunny all 

 day, with 60,377 returns, it is found that the decrease in total flight 

 on May 15, apparently due to this storm, was 9.69 per cent. Only 

 20 grams more nectar was gathered on the 16th, showing that 

 although a good day it was not quite so good a day for nectar 

 secretion as either May 13 or May 15. This indicates that the 

 afternoon storm of May 15 reduced the day's flight by from 7.40 to 

 9.69 per cent with, of course, a corresponding reduction in the day's 

 gathering compared with an optimum secretion. 



The record of July 8 (fig. 5) is typical of the flight when actual 

 precipitation occurs. This was a bright, sunny day until 12.30 p. m., 

 when a general clouding over occurred. The following data show 

 the progress of this storm : 



