4 BULLETIN 986, U. S. DEPARTMENT OF AGEICULTUKE. 



exclusively at or near the surface of the soil. In this respect the 

 larvae differ from tick larvae, which climb up on vegetation of various 

 kinds and remain in wait for a host. People frequently get chiggers 

 when they go into the grass, but our eastern species approaches from 

 the ground. The mites can be found in surface scrapings, but re- 

 peated attempts to recover them from growing vegetation have 

 failed. 2 



If chiggers attack man almost solely from the ground the question 

 may be asked, How are we to account for attachments around the 

 waist, under the armpits, and about the eyes? Again, observations 

 show that chigger attacks are seldom made above the waistline, 

 unless the clothes are quite loose around the waist, or the individual 

 has been sitting or reclining on the ground. When one simply walks 

 through a chigger-infested region, the larvae are first found about 

 the feet and ankles. Here they can be seen with a hand lens. They 

 run with great rapidity, so fast in fact that it is very hard to catch 

 them. From the ankles they spread upward, few as a rule attaching 

 here, unless the clothing is tight ; if so, many may attach. As they 

 pass upward many of the larvae either stop themselves or are stopped 

 at the garters, if these are worn below the knees. If they pass the 

 garters large numbers will attach in the space under the knees. 

 Those that pass the knees usually go as far as the waistline before 

 they attach. 



Two factors are of importance in regard to the localization of 

 chigger attachment — the tightness of the clothing at certain parts of 

 the body and the thickness of the skin. The garters around the legs 

 and the belt around the waist act as semieffective barriers. For a 

 great many minutes, sometimes for a few hours, the larvae run over 

 the skin hunting a favorable place of attachment. These rapidly 

 moving larva? are halted by the garter or belt pressure, and after 

 struggling some time either to pass through the mesh of the clothing 

 at these points or to extricate themselves may attach without further 

 search. The writer has watched these active larvae on the skin of 

 man before and after attachment and finds that tight clothing does 

 not aid them in " digging in " by furnishing a fulcrum, as has been 

 supposed. In fact, it was found experimentally that chiggers do not 

 " dig in," as has been so frequently stated, but remain attached ex- 

 ternally like a tick does. 



The thickness of the skin is of great importance in localizing chig- 

 ger attachments. Where the skin is unusually thick the larva? 

 attach with great difficulty or not at all ; and of those that do attach 



2 Dr. F. H. Chittenden has reported to the writer chigger attacks coming from over- 

 head vegetation. 'The writer has never experienced such attacks, and up to the time of 

 the preparation of this paper none had been reported to him. It may be that a second 

 species, which is relatively rare, occurs in this vicinity, as Dr. Chittenden suggests. 



