22 
THE DISPERSION OF THE GIPSY MOTH. 
very active unless the weather is warm, and when the experiments 
were conducted on cool days it was necessary to strike the box in 
which the egg clusters and caterpillars were confined in order to jar 
more of the larvae from the open end and induce them to spin down 
toward the ground. If a strong wind was blowing at the time, they 
would be caught up and blown away, and occasionally it was possible 
to see them drift 20 or 30 feet before they passed from view. Table 
I gives a summary of the data secured in these experiments. 
Table I. — Direction and velocity of wind, at Lynn Marshes, Mass., May 6 
to 12, 1910. 
Date. 
Screens. 
W 
ind. 
Average 
No 
Distance 
from 
station. 
Direc- 
Average 
tem- 
perature. 
tion. 
velocity. 
Miles 
Feel. 
■per hour. 
°F. 
1 
50 
NW. 
11 
60 
1 
100 
NW. 
11 
61 
3 
150 
SW. 
14 to 17 
66 to 70 
3 
200 
sw. 
14 to 17 
86 to 70 
3 
250 
SW. 
14 to 17 
66 to 70 
3 
300 
SW. 
14 to 17 
66 to 70 
3 
350 
SW. 
18 to 23 
63 to 67 
3 1 500 
SW. 
15 
63 
3 | 600 
SW. 
15 
66 
2 1 700 
W. 
W. 
1 1.833 
7 to 19 
51 to 66 
Number 
of larva? 
ca light. 
1910. 
May 
*Do 
May 7 
Do 
Do 
Do 
May 10 
May 11 
Do 
May 12 
Do 
The temperature records and velocity of the winds were secured 
through the courtesy of the United States Weather Bureau at Boston. 
The notes that were kept on the marshes show that the direction 
of the wind varied slightly from the Weather Bureau records, and 
the former are given above. In other respects there were probably 
minor differences, but they would not affect the result to any great 
extent. It should be noted, however, that on none of the days men- 
tioned did the wind maintain a velocity which was at all constant, 
and changes in direction were sudden and variable. This added to 
the difficulty in carrying on the experiments and made it necessary 
to change repeatedly the location of the screens. The most data 
were secured on May 7, and, by referring to the table, it will be noted 
that the weather was warmer than on any of the other days when 
tests were made ; also the direction of the wind was more constant. 
These experiments indicate that the best opportunity for the dis- 
persion of gipsy-moth caterpillars by the wind is when the tempera- 
ture is above 65° and the velocity of the wind over 15 miles an hour. 
They further show that the young larvae of this insect can be car- 
ried by the wind a third of a mile from a point less than 6 feet above 
the ground. This being the case, there is an opportunity for exten- 
sive natural spread by the wind. It is not necessary for the velocity 
of the wind to remain constant, as there is doubtless much dispersion 
