86 LIFE HISTORY OF NORTH AMERICAN TICKS. 
TaBLeE XX1I.—Engorgement of larvx of Ixodes kingt. 
Larvee dropped engorged—days following 
lication. p 
Date larvee Host Num- et ae Pease State of 
applied. ry ber. ieee — 7 __ | dropped. engorgement. 
a(s5|6[7|s|9}a3[ 14] 15] 10 
os — ——_—$—————SS | ——- —— | —_—S~™S ea ice eee | —— OS 
Sept. 15,1909 | Guinea pig.| 120] 0] 11| 51] 25| 8| 5|....|....)....}.... 100 | One-half to 
fully. 
Oct. .1,1909)| Rabbit... .|){ eA3|) dale | et a Werle Se ee Bie Ce 3 sees oe atensemeee 
Oct. 28,1909 | Bovine.....| 100] 4) 7/15] 5] 6]....].... ee | Ae -| eens 37 | One-half to 
| fully. 
Nov. 4,1909 |..... GGcesns HOON oe Weol. | On| ee |oenc | Eee as 
Nov. 16,1909 ]..... do: &: 5 10060) Ci | 25] 5) | ABE eee cee eal eeeele lee CO ates eee ee 
Jan. 14,1910 | Guinea pig.| 110] 0] O| O| 6; O| O| 2)....]...-]...- 8 | One-half to two- 
thirds. 
Sept. 28,1910 |.....do...... BOM) OO Ot Om) Rh 1 Or) nO et TOR sz 13 | One-fifth to 
fully. 
Total .| 583 |....|.... Seas Te eae as 259 
} | 
1 The larvee which dropped on this date were included with those which dropped on the following day. 
The larval molting period varies greatly, as was shown in experi- 
ments in which 54 individuals were observed, and seems to be gov- 
erned mainly by temperature conditions. The shortest molting 
period observed was 27 days; the longest, 163 days. The mean 
temperature during these two periods was 74.43 °F. and 59.65° F., 
respectively. <A total effective temperature of 821.1° F. appears to 
be required for this transformation. The large percentage of mortality 
during molting in some of the lots was probably due in part to the fact 
that a considerable number of individuals was not fully engorged 
when detached from the host. During summer, when the molting 
period is shorter, the mortality would probably be smaller, as the 
effect of drying out would not be so great. Undoubtedly humidity 
is an important factor, at this stage of their development. 
The nymph (Tables XXII-XX111).—Of 20 nymphs which molted 
to larve between January 29 and April 2, 1910, 16 were put on hosts 
during March and April. The last individual of the four remaining 
died between June 9 and July 19, 1910. Thus the longevity of these 
4 individuals was between 68 and 171 days. Another lot of 8 nymphs, 
which molted from larve between March 22 and April 4, 1910, died 
between June 9 and July 19, 1910, thus living for a period of 66 to 119 
days. The minimum nymphal engorgement period recorded was 
5 days. In one instance a nymph remained on the host 66 days, at 
the end of which time it was accidentally detached when only two- 
thirds engorged. Attachment was usually found to take place soon 
after application, but occasionally nymphs remained in proximity to 
a host for 36 hours before attaching. The readiness with which 
attachment takes place and the rate of engorgement appear to 
depend to some extent upon the vitality of the individuals when 
applied. If nymphs are weak when applied to a host they are 
usually slow in attaching, and frequently many die on the host 
