April, ’18) 
EWING AND HAETZELL: CHIGGER-MITES 
261 
The Mexican Chigger-Mite 
[Microthrombidium tlalzahuatl (Murray)] (Fig. 10c) 
The Mexican chigger mite has been known to entomologists through 
our scientific literature for half a century, and due to the efforts of 
Oudemans we now have most excellent figures of it. This mite was or¬ 
iginally described by Murray in his well-known volume on “Economic 
Entomology—Aptera” although it was mentioned earlier by Lemaire 
who has given us an account of its accidental introduction into France 
at an early date. 
The larvae are a bright yellow orange, and the body is oval in shape, 
being evenly rounded at either end. There is a single shield above; 
and the rather conspicuous palpi each end in a bifurcate claw. 
This mite is said to occur in the more temperate parts of Mexico, 
and is not found in the hot dry regions. It attacks the eyelids and 
armpits especially and apparently through predilection. The Indians, 
it is stated, remove these chiggers by means of a fine grass stalk when 
a needle is not obtainable. 
The natural hosts of the mite have not been determined, and we 
have no record of it attacking other mammals than man, but it very 
probably does. Osborn has suggested that this species may be dis¬ 
tributed over parts of the Southern States. The chiggers which the 
senior writer has so often encountered in Mississippi do not attach at 
the eyelids or armpits, but about the ankles and calves of the legs. 
The American Chigger-Mite 
[Genus? Species?] 
We have at least two species of chiggers in the upper Mississippi 
v Valley which attack man. This was shown by no other than C. V. 
Riley who obtained his original material from the superficial anatomy 
of one, Otto Lugger,—well-known American entomologist. Riley de¬ 
scribed one of these species under the name of Leptus americanus and 
the other under the name of Leptus irritans, and gave figures of each. 
The figures of Riley’s have been copied many times, and are familiar 
to most of you present at this meeting. It is almost lamentable that 
from them one can get hardly a character which is used today in specific 
diagnosis of chigger-mites. As the two mites were not reared we are 
left in doubt to this day as to their identity. 
Riley’s Leptus americanus was a very small chigger for he states: 
“This species is barely visible to the naked eye. . . It has a 
slender body, rounded behind and pointed in front. The legs were 
very long and slender. Although the present writers have observed 
many harvest mite larvae in Iowa, we have failed to find any liable 
