CHIGGERS — FARRELL 225 



the same area. There are only three records of E. peromysci 

 from shrews in other areas. It seems obvious that the spatial 

 relationships involved here could not be very great, and the record 

 shows that unattached chiggers of the two species do mingle. 

 It is possible that some character of host or parasite is operative 

 in these cases to inhibit the shrew-peromysci and the mouse- 

 blarinae associations. 



Records are incomplete with regard to areas infested on hosts, 

 but there are indications that useful characters can be determined. 

 The "rubra" group and E. peromysci have been recorded only 

 from the external auditory canal or deep in the ears of their 

 hosts. E. rubra and E. peromysci commonly infest these areas in 

 the ears of Peromyscus leucopus. In contrast, E. crateris is found 

 in small craters on the edges and the distal surfaces of the ears 

 of P. leucopus. On the same host, E. ohioensis is found attached 

 around the anal area, with some records having it distributed 

 over the abdomen, back, and legs. In these cases different species 

 of chiggers attach to different areas of a single host species. It 

 would seem that some character of the chigger is involved in 

 determining the region of attachment, which then becomes useful 

 in systematics. Another case concerns E. blarinae, which during 

 this study has been found attached only in craters over the pos- 

 terior portion of the body of Blarina. However, collectors have 

 reported it from the folds of the pinna of Sorex. Superficially, 

 this might indicate that the areas of attachment involve some 

 characteristic of the host rather than of the parasite. But collec- 

 ors have recorded Trombicula jamesoni Brennan, 1948, from the 

 ears of Blarina. This contrasts with the areas observed to be 

 infested by E. blannae on the same host and points to character- 

 istics of the chiggers as determining areas of attachment. In one 

 of the two records of E. peromysci from Blarina, the collector 

 listed the area of attachment. The chiggers were recorded from 

 the ears. However, E. blarinae also was represented in the col- 

 lection. The study is thus further complicated by the occurrence 

 of more than one species of chigger on a single host. This factor 

 must be recognized whenever any host-parasite relationship is 

 being considered as a systematic character and due precautions 

 must be taken to avoid error. It is interesting that Lawrence 

 (1949) reports that E. crocidurae in Africa is found in pits in 

 the skin of its host shrew. Further observation and study are nec- 

 essary in order to determine the systematic value of the areas of 

 attachment. 



It is apparent, even with the scanty information available, that 



