BIOLOGY AND CONTROL OF CHIGGERS. 13 
made to discover and work out the development of the causative or- 
ganism, but to no avail. 
Among the various substances that. have been employed in medica- 
tion in connection with the disease the following have been used with 
negative results: Quinine, iodine, quicksilver, arsenics, and staining 
preparations. From the beginning to the subsidence of the fever 
salvarsan and trypan red have been used with very poor results. 
An attempt has been made experimentally to utilize a serum for the 
disease, but without results. 
As chiggers are parasitic only in their larva stage and do not 
change hosts, it appears that the causative organisms must be trans- 
mitted from larva to nymph, to adult, thence to egg and to larva 
again. Such a development, although a little unusual, already has 
a near parallel in the case of the protozoan Piroplasma bigeminum, 
the organism of Texas fever, which is transmitted from mother to 
egg to larva or to nymph, in its alternate host, the North American 
fever tick, Margaropus annulatus Say. ; 
In view of what is already known in regard to the transmission of 
river fever, the biology of the chigger mites, and the general symp- 
toms following their serious attacks on man and domestic animals, 
the writer now predicts that in the next 50 years other serious dis- 
eases will be shown to be transmitted by these acarids. Should these 
mites become the transmitters of fatal diseases of domestic animals 
on a large scale it would be found that the protection of cattle or 
sheep from them would present a very difficult problem, as the mites 
are so minute and so widely distributed in woodlands and along water 
courses. 
CONTROL. 
In the case of man much protection can be had from chigger at- 
tacks by properly clothing the lower extremities or by the application 
of repellents either directly on the skin or on the under garments. 
PROTECTION AGAINST CHIGGER ATTACK. 
Since the unengorged larve are not over 150y in width, it is seen 
that they can pass through the mesh of many kinds of garments; 
it is easy, however, to wear those of a weave tight enough to prohibit 
the larvee from passing directly through the cloth. The employment 
of tightly woven cloth, or other materials which are impervious to 
the larve, nevertheless, is not enough. These garments must be worn 
so as to fit tightly around the edges or the larvee will yet have an 
avenue of entry. 
It was frequently noticed that half-shoes exposed the ankles, and 
for that matter indirectly the whole body, to much more serious 
*The control of chiggers affecting poultry is considered in Farmers’ Bulletin 801. The 
measures given in the fresent bulletin have reference more particularly to chiggers as 
parasites of man. 
