HARVEST MITES, OR ‘‘CHIGGERS.’’ 3 
after which the surrounding surface becomes congested, the affected 
area spreading until it is from less than a fourth to a half or three- 
fourths of an inch in diameter. This congestion may manifest itself 
within less than an hour after exposure or may not be apparent for 
12 hours or so, the fever being at its height usually on the second 
day. The symptoms are apt to be first noticed when the sufferer has 
removed his clothing at night, or upon awakening from sleep. It 
sometimes happens that there is little irritation until some time after 
exposure, but with most persons susceptible to the poisonous effects 
of these mites irritation is first experienced on the second day. The 
feverish appearance of the afflicted skin area varies according to the 
susceptibility of the person attacked. Children dwelling or sojourn- 
ing in mite-infested localities suffer greatly from these pests, ex- 
periencing more severe annoyance than 
adults, and young women as a rule suffer 
more than older persons. People with 
thin, delicate skin and florid complexion 
are most afflicted by the mites, and with 
them the congested red spots are propor- 
tionately larger and more inflamed and 
irritating. 
Many persons, however, as, for example, 
permanent residents of infested regions, 
and particularly farm laborers, seem to be 
practically proof against the toxic effects 
of harvest mites and go with impunity 
into places overrun with them. This im- 
munity to poisoning is obviously due to 
two causes: (1) To outdoor work which 
toughens the person’s skin, especially such 
portions of the arms and legs as are much exposed to the sun and 
weather; and (2) to inoculations, due to frequent infection. 
The inflamed spots due to the presence of the mites under the human 
cuticle are often diagnosed as hives, nettle rash, urticaria, or the 
“wheals,” and resemble closely those produced on many persons by 
the “bites” of fleas and some mosquitoes, but on the second or third 
day each of the mite-infested areas is usually found surmounted at 
the middle by a minute vesicle or water blister. This is obviously 
the most important characteristic of harvest-mite attack. After the 
subsiding of the inflammation and itching, which takes place in a few 
days, a small scale or scab frequently forms, leaving on some persons 
a scar which does not wholly disappear in extreme cases for weeks. 
The mites naturally attack first those portions of the body which are 
most exposed—those nearest the ground. They crawl into the 
-" 
Fic. 3.—Trombidium sp.: Adult, high- 
ly magnified. (From Banks.) 
