OUR ONLY COMMON NORTH AMERICAN CHIGGER, ITS 
DISTRIBUTION AND NOMENCLATURE 1 
By H. E. Ewing 
Specialist in Arachnida, Bureau of Entomology , United States Department of 
Agriculture 
Since beginning the study of our North American chiggers a few years 
ago the writer has collected many specimens in different parts of the 
United States, and in addition has received many more specimens from 
various entomologists. It is believed that these collections have been 
sufficiently numerous and diversified geographically to give a good index 
to the occurrence and distribution of our chiggers. 
The outstanding fact that has been established by the study of these 
chiggers is that in nearly all localities the common species attacking 
man and domestic animals is Trombicula tlalzahuatl (Murray). This 
species is now known to occur from Long Island to central Mexico and 
from the Atlantic coast to the Rocky Mountains. It has been found on 
lands actually flooded at times by marine tide waters and also occurs well 
up in the Appalachian Mountains. In the more humid southern part of 
its range the mite is found almost everywhere where there is rough growth 
of woods or shrubbery. Toward the northern limits of its range the 
species occurs only in isolated “islands” where the local conditions are 
favorable for its maintenance. 
This common species of the United States, so long known yet so little 
studied, appears to be no other than the well-known Mexican chigger with 
the unpronounceable specific name which is spelled two ways, either 
tlalzahuatl or tlalsahuate. This species should be referred to the genus 
Trombicula, not to Microthrombidium, as has been done by different 
workers in the past. For a long time the writer had been of the belief 
that our chigger of the Atlantic seaboard and lower Mississippi Valley 
was tlalzahuatl , but it remained to get further evidence before coming 
to a definite conclusion. This was obtained recently when an examina¬ 
tion was made of many specimens from Texas and other Southern States. 
Not only is our common chigger species found over apparently the whole 
of the Gulf States, except of course where local conditions prohibit, but 
it increases in its abundance as the coast is approached; and at points in 
Texas as far south as Houston the writer has found infestation in maxi¬ 
mum proportions. Thus the conclusion is justified that the same species 
ranges far to the southward, in fact into the moist lowlands of Mexico, 
where, tlalzahuatl has long been known. 
In 1912 Oudemans 2 gave good drawings and a good description of 
tlalzahuatl , types of which are now in the Trouessart collection. Until 
this description appeared it would have been impossible to recognize the 
Mexican chigger without actually seeing specimens of it. By comparing 
specimens of our common chigger with Oudeman’s figures and description 
1 Accepted for publication August n, 1923. 
2 Oudemans, A. C. 1912. die bis jetzt bekannten darven von thrombidiidae und erythraeidae. 
In. Zool. Jahrb., Sup. 14, p. 18-24, fig. D. 
(401) 
Journal of Agricultural Research, 
Washington, D. C. 
ahw 
Vol. XXVI, No. 9 
Dec. 1, 1923 
Key No. K-116 
