16 BULLETIN 986, IT. S. DEPARTMENT OF AGRICULTURE. 



A well-known golf course was laid out west of the District of 

 Columbia in a region heavily infested with chiggers. Later an 

 investigation showed that the sodded areas where the balls were 

 played were quite free from chiggers. When persons went into the 

 patches of rough growth between or around these areas they were 

 attacked by chiggers. 



A chigger-infested lot in East Falls Church, Va., was cleared of 

 rough growth and a house put on it during the summer of 1919. 

 These operations destroyed the breeding places of the chiggers. 



Of all the growths that favor the harboring of chiggers none is 

 more favorable than wild blackberries or wild dewberries. Wild 

 blackberry patches in Virginia and Maryland invariably were found 

 to harbor immense numbers of chiggers. Where such patches are 

 located at very objectionable places their obliteration would seem 

 justified. The fruit produced by these wild canes is of a good quality, 

 however, and constitutes not a small item in the summer food supply 

 of the country; hence a wholesale destruction of wild blackberries 

 would be both rash and foolish. 



Dr. Chittenden has mentioned (2) the value of cattle and even 

 of the passing of many persons in destroying chiggers. In 1914 (3) 

 he published the results of a conversation which he had with Mr. 

 William N. Irwin (through an error given as E. F. Erwin), 

 who before his death was connected with the Department of 

 Agriculture; in this conversation Mr. Irwin stated that he con- 

 sidered cattle inadequate where a large area was to be dealt with. 

 He claimed, however, that he had experienced good results where 

 sheep were used instead of cattle. The efficacy of sheep in chigger 

 eradication thus being shown, an explanation of their agency and its 

 effect on the chiggers is due. Dr. Chittenden claimed that the value 

 of cattle in chigger control came from the trampling of the pests, 

 and he would explain in the same way the benefits from the utiliza- 

 tion of sheep, adding, however, that the sheep are probably more 

 effective, by " keeping the grass more tightly cut than would cattle." 

 Mr. Irwin explained the agency of the sheep as being due in part 

 to the ascent of their legs by the chiggers and their destruction 

 through contact with the oil in their wool. The present writer would 

 explain this observed difference between the efficacy of cattle and 

 sheep as being due chiefly to the food habits of the latter, the sheep 

 not only keeping the grass more closely cropped, but also feeding 

 to a considerable extent on the leaves of shrubbery. 



Just what the value of a certain amount of shrubbery is to chig- 

 gers is not known in the case of our species. It may furnish a favor- 

 able environment for the natural hosts of the parasites, or furnish 

 the necessary environment for either the nymphs or adults of the 

 chiggers, or both these instars, or furnish a proper environment for 

 the larvae. 



