24 THE DISPERSIOX OF THE GIPSY MOTH. 
lion will show that this consists of silk which the larva has spun, 
and it is probable that this acids to the buoyancy of the insect if it is 
caught up by the wind. 
As the method of using the reel gave very poor results, two sets 
of experiments were carried on by Mr. C. W. Stockwell in the lab- 
oratory. He induced the caterpillars to spin, and attached the thread 
to the end of a stick 1 yard long. As the insect lowered itself, the 
thread was measured with the stick by raising and inverting it, and 
thus the larva was prevented from spinning to the floor of the room. 
In the first set records were secured from 18 newly hatched larva? 
that had not fed. The quantity of silk spun ranged from 7 feet 6 
inches to 25 feet 6 inches, averaging 17 feet. Fourteen records were 
then secured from larva? 3 days old, and the silk ranged from 12 
feet to 63 feet 5 inches, with an average of 31 feet. 
The results of these tests show that there is much individual varia- 
tion in the quantity of silk that caterpillars will spin, and it is prob- 
able that under favorable outdoor conditions much more would 
be produced than is indicated by the averages given. 
If 20 to 30 feet of silk is spun by a larva it will undoubtedly help 
it to remain in the air in case the thread is broken by the wind, and 
will probably add buoyancy to the insect and thus increase the dis- 
tance that would ordinarily be covered by wind spread. 
RELATION OF TEMPERATURE TO HATCHING OF EGGS. 
Temperature has a very important relation to the hatching of 
insect eggs; hence the time of larval appearance varies from year to 
year. Gipsy-moth eggs begin to hatch the last week in April, but 
the hatching is often deferred a week or more. Owing to the warm 
weather in March, 1910, hatching took place in the field as early as 
April 3, but the bulk of the eggs did not hatch until much later. In 
the case of the gipsy moth — and the same principle governs in the 
case of other insects which winter in the egg form — it is possible to 
secure hatching in the winter if the eggs are kept in a warm room. 
The length of the period of high temperature which is required to 
hatch them varies with the season of the year. For example, gipsy- 
moth eggs collected late in December and kept at a temperature of 
from 70° F. to 80° F. will hatch in about 15 days, while if the 
same collection is made in March hatching will take place in about 
half the time. This shows that as the normal time for hatching ap- 
proaches it requires a shorter period of warm weather to bring out 
the larva?. 
During the past four years the first date of finding gipsy-moth 
larva? in the field in Massachusetts was, in 1908, April 22 : 1909. April 
22; 1910, April 3; 1911, April 28. The data for 1908 were furnished 
by Mr. TV. F. Fiske. The other dates were secured from field reports 
