256 
JOURNAL OF ECONOMIC ENTOMOLOGY 
[Vol. 11 
THE CHIGGER-MITES AFFECTING MAN AND DOMESTIC 
ANIMALS 
By H. E. Ewing and Albert Hartzell, Ames , Iowa 
Although the chigger-mites are widely known over the world on 
account of their attacks on man and domestic animals, yet, because 
of their minute size, they have been remarkably exempt from thor¬ 
ough investigations which usually have been applied to pests of so 
much economic importance. In Europe, due chiefly to the work of 
Dr. Oudemans and to Berlese, we have recently learned much of the 
taxonomy, biology, habits, and distribution of the foreign chigger- 
mites. 
As is well known among entomologists, chigger-mites are the larvae 
of the brilliantly colored harvest mites, which, according to acarolo- 
gists, are placed in the family Trombidiiml This fact, however, 
was not known when many of our common chiggers were first de¬ 
scribed, or if known was not heeded. When these early descriptions 
were made, the larval characters of real taxonomic importance had not 
been worked out, so that these descriptions have proved to be all but 
valueless to us today, notwithstanding we now have an excellent key 
to the chiggers based on larval characters. 
In this paper it has been the object of the writers to give a summary 
of the important biological and other facts concerning the chigger- 
mites known to affect man and domestic animals, together with ref¬ 
erences to a few important species found in this country which so far 
have not been recorded from these hosts. To the recorded observa¬ 
tions of others we will add what we have learned of our American 
chiggers. Some of the species here mentioned have not been suffi¬ 
ciently known in the past to have acquired common or popular names, 
hence one of our chief tasks has been to get appropriate common names 
for these less known chigger-mites. 
The Summer Chigger of Europe 
[Metathrombium poriceps (Oudemans)] (Fig. 10a) 
Chigger-mites have been studied more in Europe than in America, 
and it is now known that at least three different species are concerned 
in the attacks upon man and domestic animals. Of these three species, 
two are quite common, one attacking in the summer time, the other in 
the fall. 
The summer chigger-mite of Europe is a very small creature not 
more than 0.4 mm. in length when unengorged. It is egg-shaped, and 
has above on the thorax two porous chitinous plates or shields. 
