DISPERSION OF GIPSY-MOTH LARVAE BY THE WIND. 
21 
Table VIII is here presented to show the annual advance of the 
moth before and after control was attempted. This indicates that 
the winds are chiefly responsible for the present conditions. 
Table VIII. — Spread of the gipsy moth in various directions by series of years from five 
■ years after its introduction at Medford, Mass., to 1914. 
Average spread 
Periods of years. 
NE. 
N. 
NW. 
W. 
SW. 
S. 
SE. 
per year by 
periods. 
Miles. 
Miles. 
Miles. 
Miles. 
Miles. 
Miles. 
Miles. 
Miles per year. 
1875-1890 
15 
10 
5 
10 
6 
4 
3 
0.5 
1891-1899 
5 
4 
5 
4 
• 4 
5 
4 
.5 
1900-1905 
27 
11 
12 
10 
12 
14 
62 
3.5 
1906-1909 
41 
60 
25 
19 
15 
16 
11 
6.7 
1910-1914 
114 
16 
28 
15 
24 
26 

6.4 
Total 
202 
101 
75 
58 
61 
65 
80 
Average for 40 years 
2.3 
Average spread per year in 
5 
2.5 
1.9 
1.5 
1.5 
1.6 
2 
It will be noted that the spread from the original center was very 
slow, averaging only 0.5 of a mile per year up to the beginning of the 
campaign in 1890. It was then held in control for a period of about 
nine years, during which time there was very little advance into new 
territory. The conditions in the old infested area were also much 
improved. This shows the necessity for keeping the moth under 
complete control if windspread is to be prevented. During the 
period from 1900 to 1905, when no work was being done, the moths 
spread at the rate of 3.5 miles per year. This had increased to 6.7 
miles per year from 1906 to 1909, but this ratio has decreased to 
some extent in the last period up to 1914, inclusive. 
The greatest distance gained in various directions has been to the 
northeast, an average of 5 miles per year for 40 years, which is the 
result of the favorable southwest winds. The combination of south- 
east and southwest winds during the dispersion period has carried 
the larvae northward at the rate of 2.5 miles per year. The spread 
to the west, southwest, and south was accomplished at a slower rate, 
owing to the less favorable winds blowing in those directions. 
SUMMARY. 
In 1913, as a result of the several experiments conducted by using 
tanglefooted screens and cloth for traps, there were caught on 977 
square feet 289 first-stage larvae which had been borne by the wind 
one-eighth to 1 mile or more. In 1914 there were removed from 
1,614 square feet of sticky surface 346 larvae which had been blown 
from one-eighth to 13J miles or more, as verified by the wind records 
taken at or near those points. Three larvae were also taken from 
two large screens on the hills in New Hampshire during 1914. 
