BIOLOGY AND CONTROL OF CHIGGERS. 5 



many can not remain attached during the body movements of the 

 host or are not able to reach the lymph supply of the true skin and 

 engorge. Of the thousands of chigger attachments observed by the 

 writer, not a single one was found on the calloused parts of the 

 hands or feet. 



HOSTS. 



It was the belief of earlier entomologists that chiggers lived upon 

 the juices of plants. That C. V. Riley shared this common belief is 

 evident from the following statement (10) which he made in regard 

 to one of his species : 



The normal food * * * must, apparently, consist of the juices of plants 

 and the love of blood proves ruinous to those individuals who get a chance to 

 indulge it. 



When it was learned by actual rearing experiments that several of 

 the species of Trombidiidae were normally parasitic on terrestrial 

 tracheates, this older theory was dropped, and it was commonly as- 

 sumed, and frequently stated, that the chigger larva? were normally 

 parasitic on insects and closely related invertebrates. This belief 

 was equally shared by the mite specialist and the general ento- 

 mologist ; but that the chigger larvae could be normally parasitic on 

 vertebrates was never suspected; in fact, the references to their 

 " death feast " on man or domestic animals continued as numerous 

 as before. 



When the writer began, in the summer of 1919, his search for the 

 natural host of the species occurring in Virginia and Maryland, he 

 collected all insects found parasitized with trombidiid larvae. These 

 larvae were examined to see if any of them belonged to the species 

 attacking man, or were in fact true chiggers. Although many in- 

 sects and other tracheates were found parasitized, in no instance did 

 these parasitic larvae prove to be the species attacking man. 



Not satisfied with this method of investigation, another was in- 

 stituted. On some vacant lots that had grown up to a considerable 

 extent in blackberries and which were very heavily infested with 

 chiggers (over a hundred attached in less than two hours), insects of 

 all kinds were collected. There were hundreds of them and scores 

 of species. 



These insects were taken to the laboratory and examined both 

 alive and after killing in cyanide bottles, and in no case was a 

 single specimen of our eastern chigger found. The sweepings and 

 other collections were so thorough that this observation convinced 

 the writer that the chigger found in the vicinity of Washington is 

 not a normal parasite on terrestrial tracheates that live above the 

 ground. 



