76 THE HOUSE FLY—DISEASE CARRIER 
family Trombidiidae, but the adult has not been reared 
and is still unrecognized in Europe. Riley found these 
harvest mites on house flies in Missouri, in some years 
so abundantly, he says, that scarcely a fly could be 
caught that was not infested with some of them cling¬ 
ing tenaciously at the base of the wings. Later he suc¬ 
ceeded in rearing the adult, and described it as Trom- 
bidiutn muscarum. In recent years Oudemans has de¬ 
scribed Trombidium niuscce from larval mites found 
on house flies in Holland. 
“All these forms are minute, six-legged, red mites, 
which cling to the body of the fly and with their thread¬ 
like mandibles suck up the juices of the host. They are 
nearly related to the so-called ‘red-bugs,’ or ‘chig- 
gers,’ of the Southern United States. When ready to 
transform, they leave the fly and cast their skins, the 
mature mite being a free-living, hairy, scarlet creature 
about one and five-tenths mm. long. The adults are 
usually found in the spring and early summer, while 
the larvae are usually found in the autumn on house 
flies and other insects. 
Mites of the genus Pigmeophorus, of the family 
Tarsonemidae, have also been taken on house flies. 
They cling to the abdomen of the fly, but it is not cer¬ 
tain whether they feed on the insect or use it simply 
as a means of transportation. The hypopus, or mi- 
gratorial nymphal stage of several species of Tyro- 
glyphus, has been found on house flies. This hypopus 
attaches itself by means of suckers to the body of any 
insect that may be convenient. The mites do not feed 
