90 THE PERIODICAL CICADA, 
each degree of difference in the average summer temperature, whether 
it be due to latitude or elevation.¢ 
An interesting case of artificial acceleration in the appearance of 
these insects is recorded by Professor Riley as follows: Dr. E. S. Hull, 
of Alton, Ill., having placed some underground flues for forcing vege- 
tables, the unnatural heat caused the cicadas to emerge by the 20th 
of March and from this time on until May. Other instances of accel- 
eration are given in the discussion of the subject of retardation or 
acceleration in times of appearance as an explanation of the forma- 
tion of the different broods. (See p. 24.) 
Notwithstanding the difference in time of emergence in the above 
citations, the fact nevertheless remains true of the great uniformity 
evidenced in the time of emergence, namely, the last week in May, for 
the great bulk of the territory covered by the different broods of the 
Cicada, and this fact is one of the noteworthy features in the life his- 
tory of the insect. 
The males precede the females by several days and disappear earlier 
in the summer, both by reason of being shorter lived and also on 
account of their earlier appearance, so that it often happens that while 
the woods are still filled with females actively engaged in ovipositing, 
the males are altogether absent and their songs are unheard. 
DURATION OF THE ADULT STAGE. 
Under normal conditions the Cicada remains in evidence in the 
woods five or six weeks, occasional individuals occurring later, but as 
a rule their disappearance is almost as sudden as their appearance and 
is complete in the first weeks in July. Mr. Butler, writing of the 1885 
brood in Indiana, says that twenty-three days after the appearance of 
the Cicada a perceptible decrease in numbers was observed, chiefly 
from a disappearance of the males. On July 15, nine days after they 
had disappeared from the river valley districts, they were still abun- 
dant and active in more elevated situations. Mr. Davis, writing of 
the brood of 1894 on Staten Island, says that by the third week in 
June the cicadas commenced to die of old age, and yet the males were 
still singing and the females were abundant in certain localities as 
late as the 8th of July, while by the 15th of the same month all had 
disappeared. 
Mr. Hopkins found on the hills near Morgantown, W. Va., that the 
dates of the Cicada appearance were about normal, the first adults 
appearing on May 20, the first general appearance not coming, how- 
ever, until the 24th. Cold weather mtervening, there was a subsid- 
ence again until the 30th, when they emerged again in enormous 
@ Bulletin 50, W. Va., Agric. Exp. Station, p. 17. 
