70 
Parasitic Arthropods 
There is a very striking sexual dimorphism in this species. The 
non-gravid female is elongate, about 2009, by yojx (fig. 52), with the 
abdomen slightly striated longitudinally. The gravid female (fig. 53) 
has the abdomen enormously swollen, so that it is from twenty to a 
hundred times greater than the rest of the body. The species is- 
viviparous and the larva' undergo their entire growth in the body of 
the mother. They emerge as sexually mature males and females 
which soon pair. The male (fig. 54) is much smaller, reaching a 
length of only 3 20^ but 
is relatively broad, 
8c| jl, and angular. Its 
abdomen is very great¬ 
ly reduced. 
As far back as 1850 
it was noted as caus¬ 
ing serious outbreaks 
of peculiar dermatitis 
among men handling 
infested grain. For 
some time the true 
source of the difficulty 
was unknown and it 
was even believed that 
the grain had been 
poisoned. Webster 
has shown that in this 
country (and probably 
in Europe as well) its 
attacks have been mistaken for those of the red bugs or “chiggers” 
(larval Trombiidse). More recently a number of outbreaks of a 
mysterious “skin disease” were traced to the use of straw mattresses, 
which were found to be swarming with these almost microscopic 
forms which had turned their attentions to the occupants of the beds. 
Other cases cited were those of farmers running wheat through a 
fanning mill, and of thrashers engaged in feeding unthrashed grain 
into the cylinder of the machine. 
The medical aspects of the question have been studied especially 
by Schamberg and Goldbergcr and from the latter’s summary (1910) 
we derive the following data. Within twe ve to sixteen hours after 
exposure, itching appears and in severe cases, especially where expo- 
