16 BULLETIN 273, U. S. DEPARTMENT OF AGRICULTURE. 
Xear the tank were a few low trees consisting of white pine and 
gray birch; these were cleaned of egg clusters and the trunks tangle- 
footed in order to prevent the larvae resulting from overlooked egg 
clusters getting into the tops of the trees. The country about this 
hill on all sides is generally infested (PL VI), so that almost all winds 
tempered to 50° F. or above bore caterpillars. The weather data 
used for comparison with the daily catch here was taken at Plum 
Island, about 10 miles east. 
Table VI. — Dates and numbers of caterpillars removed from screen at Merrimac, Mass., 
in 1914; also general direction of the wind during the period. 
Date and time removed. 
Number 
borne by 
west 'winds. 
Number 
borne by east 
and south 
winds. 
Direction of wind at time of examinations 
few hours previously. 
Mav 19, p. m 
Mav 20, p.m. 
Mav 21 
May 22, p. m . 
May 23. p. m 
May 24. p. m 
Mav 25. p. m. 
Mav 26 
May 27, p. m 
Mav 27, p. m 
Mav2S, p.m. 
May 29 
Mav 30, p. m 
May 31 
June 1, p.m. 
June 2, p.m. 
Total.. 
NW. and W., 8 a. m. to 5 p. m. 
NW. and W., May 19, 8 a. m., to May 20, 2 p. m. 
NE., E., and SE., May 20, 3 p. m., to May 22, 5 
p. m. 
W., NW., and SW., May 23, 8 a. m., to May 27, 
10 a. m. 
Do. 
Do. 
Do. 
Changed to S., Mav 27, 11 a. m, to 5 p. m. 
W. and NW., May 28, 8 a. m. to 5 p. m. 
SW. and W., May 30, 8 a. m., to June 1, 11 a. m. 
S. and SE., June 1, 12 m. to 5 p. m. 
W. and NW., June 5, 8 a. m., to June 6, 5. p. m. 
1 Some of these larvae were caught before this date, as 7 were dead on removal. 
2 No examination. 
3 Number accredited to different winds estimated owing to changes in direction. 
One hundred and forty-one larvae were trapped on this screen of 
144 square feet between May 19 and June 2, inclusive. A few of these 
undoubtedly were blown on before May 19, as seven of the nine were 
dead on removal, indicating that the aviation of the small larvae 
began probably two or more days earlier in Merrimac than along the 
seacoast. 
With apparently an equal infestation on ail sides of this screen 
one-half mile or more distant, almost twice as many larva? were 
trapped as a result of prevailing winds from the west as from the east, 
The data secured in this experiment indicate that all winds during 
the day in a section generally infested bear caterpillars excepting the 
north, which was not recorded during this period. Considering that 
practically one larva was caught per square foot 300 feet above sea 
level, it is only by conjecture that we can estimate the maximum 
height reached by them and the length of time they remain suspended 
under average conditions. It is a known fact that large numbers of 
