BIOLOGY AND CONTROL OF CHIGGERS. 9 
ing the actions of larve’ with high-power objectives after they had 
been removed with a “slice” of epidermis. They wriggled first 
one way, then another, pulled with all their strength backward and 
forward, gave side twists, and in fact strained in almost every pos- 
sible way until released. One individual was timed during this 
process, and it took it seven minutes to free itself from the hold it had 
obtained on the epidermis. 
These observations were repeated upon a lot of 16 individuals for 
nine successive days. They were numbered as before, and daily ob- 
servations made upon them. Not only did none of 
these larvee burrow into the skin, but they remained 
attached only by their mouthparts and engorged 
like ticks. Later they released this hold and fell off. 
DO CHIGGERS ENTER THE PORES OF THE SKIN? 
Some authorities, while not believing that chig- 
gers burrow into the skin, yet hold that because 
of their minute size they enter the pores and thereby 
cause much inflammation and other injury. This 
point has been carefully investigated. Of the 26 
numbered individuals that were observed and stud- 
ied daily, 21 were attached to the smooth surface 
of the skin, while 5 were attached at the bases of 
hairs, each having the capitulum thrust into the 
mouth of the hair follicle as shown in figure 4. 
Not a single one had penetrated a pore or hair 
follicle. HG, ~4.—— Slice; 
fj ¢ 3 of epidermis from 
The species occurring in the northeastern part of 
the United States shows a tendency to attach at the 
mouth of hair follicles. It may be that the larvee 
actually try to enter. They are prevented, however, 
from doing so under normal conditions of the skin 
the skin of calf 
of leg showing 
method of at- 
tachment of east- 
ern chigger in 
mouth of hair 
follicle. 
by the small diameter of the follicles themselves. 
-For this same reason it would be impossible for chiggers to enter the 
pores of the skin, unless the latter were greatly dilated as a result of 
some skin trouble. In diameter the pores of the skin range from 
20 to 50 », according to Piersol. The width of an unengorged larva 
from either the western or eastern part of this country is approxi- 
mately 150 ». Thus it is seen that unless the pores were unusually 
dilated the mites could not enter if they would. 
In the case of persons who have just cleaned out the pores of the 
skin after a long period of negligence, it would be possible for the 
mites to enter some of them, as, for example, pores dilated by come- 
dones. The writer has observed such pores dilated until they were 
55672°—21—Bull. 986-——2 
