282 JOURNAL OF ECONOMIC ENTOMOLOGY [Vol. 11 
to attack man, which look similar to Riley’s drawing of his Leptus 
wnericanus. 
Riley states that this mite infests chiefly the scalp and armpits, 
that it does not bury itself in the flesh, but simply insinuates the ante¬ 
rior part of its body under the skin. The method of attack given by 
Riley at once suggests the Mexican chigger, but if you will compare 
Riley’s figure with Oudeman’s drawing of the Mexican chigger you 
can see at once that they are different species. The Mexican chigger 
is a broad, stout species, with moderate legs, while Riley’s drawing of 
americanus shows the legs longer than the body. We know nothing of 
the natural hosts of the mite or if its distribution other than that it is 
found in the upper Mississippi Valley. 
The Irritating Chigger-Mite 
[Genus? Species?] 
This species, which has long gone under the name of Leptus irritans 
Riley, has been most frequently mentioned in our American literature. 
Riley says of it: “This is the most troublesome and perhaps best 
known of the two (the other species being his Leptus americanus ) caus¬ 
ing intense irritation and swelling on all parts of the body". . . .” 
We have made many attempts to place this species of Riley’s but have 
failed. It can not be placed even in the proper genus, as we recognize 
the genera of Trombidiid^e today. 
The irritating chigger according to Riley’s figure and description is 
of minute size, but has a broad body and very large palpi. Indeed 
the palpi, as shown in Riley’s figure, are larger in proportion to the 
body than in any of our known species. 
Since Riley, as well as others, speaks of this chigger as being so com¬ 
mon and so* troublesome it may be thought by some that it is no other 
than our common locust chigger so frequently found on the wings of 
grasshoppers in the upper Mississippi Valley. This point has been 
tested here at Ames by letting these locust chiggers crawl over the 
bare arms and legs without effect! Individuals have gone through 
grass heavily infested with these locust chiggers with the trousers 
rolled up at the bottom and with the socks rolled down at the top, but 
without a single attachment. Many men have been observed work¬ 
ing in areas infested with these chiggers, but they have not complained 
of being attacked. Just what species Riley’s irritans will prove to be 
we cannot say. It very probably will never be known for a certainty. 
The Locust Mite 
[Euthrombidium trigonum (Hermann)] (Fig. 10 d, e, f, g, and h ) 
The larvae of this species were first reported from Omaha, Nebraska, 
