BIOLOGY AND CONTROL OF CHIGGEES. 17 



It has been stated that the cropping or mowing of grass lets in 

 more sunshine and in this manner destroys the chiggers. This can 

 hardly be the case, however, as larvae have been handled and exposed 

 frequently in the bright sunshine and no ill effects to them noted. 

 In the field also, where there is only a scant growth of dewberries and 

 an abundance of sunshine chiggers may be found in great numbers. 



Chiggers . are almost semiaquatic and will endure frequent sub- 

 mergence. In the laboratory they do well, if not their best, in an 

 atmosphere near saturation. This humidity requirement will help 

 explain the advantage of a rough growth to the species, which lives 

 almost exclusively at the surface of the ground. In most situations 

 it may be that the moisture is only sufficient when the ground is 

 clothed with a considerable growth of vegetation. Thus the effect 

 of sunshine would appear to be indirect and to destroy the chiggers 

 in most situations where allowed to act by drying the surface of the 

 ground. 



DESTRUCTION OF THE CHIGGERS THEMSELVES. 



It is stated that chiggers may be destroyed by a liberal applica- 

 tion of sulphur to the field. The use of 50 pounds to the acre has 

 been recommended. For this purpose a dust gun or dust blower 

 could be used to advantage. On lawns the use of sulphur is un- 

 necessary, as chiggers will automatically disappear if the grass is 

 kept cut short. 



Chiggers may best be destroyed on the body of man before they 

 become attached or very soon afterwards. If one knows that there 

 has been exposure to chigger attacks the shins and ankles should be 

 examined with a hand lens for the active larva? even before any itch- 

 ing sensation is felt. Only a few of the active larvse will be observed. 

 They will be seen to run over the skin very rapidly and can not be 

 captured to advantage. 



Larvse on the body can be easily killed by the application of an 

 acaricide. Various substances applied at the time of bathing have 

 been recommended. On August 10, 1919, after exposure to 

 chigger attacks, a thick lather of soap was applied to the affected 

 parts. The lather was allowed to remain for 10 minutes and was 

 worked continually over the skin. After 10 minutes it was washed 

 off. Examination next day failed to reveal any chiggers and no 

 itching developed. 



On August 18, 1919, after exposure at Somerset, Md., and after 

 larva? had attached, the same application of thick soap lather was 

 tried. On the 19th much itching was felt, yet no chiggers were 

 found. Apparently the soap had acted as an acaricide but not as a 

 palliative. 



