UNITED STATES DEPARTMENT OF AGRICULTURE 



BULLETIN No. 986 



ilr . .. _ . _ . . *§ 



Contribution from the Bureau of Entomology 

 L. O. HOWARD, Chief 



.SW^NS?^ 



Washington, D. C. 



December 3, 1921 



STUDIES ON THE BIOLOGY AND CONTROL OF 



CHIGGERS. 



By H. E. Ewing, Specialist in Mites. 



CONTENTS. 



Page. 



Introduction 1 



Species concerned 1 



Notes on seasonal history 2 



Local distribution 3 



Habits of unattached larvae 3 



Hosts 5 



Injury 7 



Cbigger injury confused with 



many other kinds of injury ' 7 



Do chiggers penetrate the skin? 8 

 Do chiggers enter the pores of 



the skin? 9 



Difference in susceptibility 10 



Page. 

 Injury — Continued. 



Local injury 10 



General disturbances 11 



Relation to disease 12 



Control 13 



Protection against cbigger at- 

 tack 13 



Destruction of breeding places_ 15 

 Destruction of the chiggers 



themselves 17 



Palliatives 18 



Literature cited 19 



INTRODUCTION. 



Notwithstanding the obvious economic importance of chiggers, 

 and an almost universal acquaintance with their injury, little has 

 been done in the past to ascertain their habits in nature or to find 

 efficient methods for their control. Because of these facts the writer 

 decided early in the season of 1919, with the approval of Dr. L. O. 

 Howard, Chief of the Bureau of Entomology, to begin a series of 

 experiments and observations on their biology and control. The 

 work was started in June of that year and continued until the fall of 

 1920. For various reasons it was thought advisable to discontinue 

 the work then for some time, hence the results thus far obtained have 

 been prepared for publication. It is the expectation of the writer, 

 in the near future, not only to complete the life history for at least 

 one of our species, but to give a synopsis of the taxonomy and dis- 

 tribution of the species occurring in the United States. 



SPECIES CONCERNED. 



Years ago C. V. Riley (10) 1 described from this country ("south- 

 western States ") two chigger species under the familiar names of 



1 Reference is made by number (italic) in parentheses to " literature cited," page 19, 

 55672°— 21 1 



