264 
JOURNAL OF ECONOMIC ENTOMOLOGY 
[Vol. 11 
The House-fly Chigger 
[Thrombidium muscarum Riley] (Fig. 10 i, j ) 
The larvae of this species were recognized by Riley, in 1875, as 
A stoma parasiticum Latreille. Two years later a description of it was 
published in the Report of the United States Entomological Commission 
as a new species under the name Trombidium muscarum Riley. We 
have carefully examined the larva of his form and believe that the 
species is valid, and should be retained in the genus Thrombidium. 
This genus may be distinguished by the presence of two median dorsal 
shields. The front shield is furnished with eight setae and has longi¬ 
tudinal striations. 
During some seasons scarcely a house-fly can be found that is not 
infested with a number of these mites. Riley succeeded in rearing 
the adult. The senior writer has also reared the adult of this species. 
As far as known this mite is confined to a single host, Musca domes- 
tica . It could never be induced to attach to man. Apparently this 
chigger is generally distributed throughout the United States. We 
have records from New York, Illinois and Iowa. 
Summary 
1. Six separate and distinct species of chigger-mites taken from man 
and domestic animals have been accurately described, figured and 
named. Three of these are found in Europe, two in the East Indies 
and one in Mexico. 
2. At least two distinct chigger-mites are known to attack man in 
this country. We have been unable to place either one of these species 
in our modern classification of the chigger-mites, and are in doubt in 
regard to their specific identity. 
3. The common locust mite in the United States is the same as the 
common locust mite of Europe, hence Trombidium locustarium Walsh 
is a synonym of Euthrombidium trigonum (Hermann) of the old world. 
Observations and experiments have shown that this species does not 
attack man. 
4. The scientific name of our house-fly chigger, Thrombidium mus¬ 
carum Riley, still stands, the species being good. 
5. Only two species of our American chigger-mites have been 
reared to maturity. 
6. A thorough survey of our chigger-mite fauna, with notes on hosts 
and geographical distribution is most needed at present. 
