BULLETIN 986, TJ. S. DEPARTMENT OF AGRICULTURE. 



Leptus americanus and Leptus irritans. Although these names have 

 been used frequently in American literature dealing with economic 

 entomology, and the figures of Riley's two species often copied, the 

 present writer is bound to confess that after studying carefully 

 Riley's descriptions and figures and some of his microscope slides 

 (types?) he has been unable to correlate either americanus or irritans 

 with the two species with which he is familiar. Further than this, it 

 can now be fairly definitely stated that americanus is not a species of 

 Trombidiidae at all, but is rather a species of the family Eryth- 

 raeidae, a group to which the genus Leptus really belongs, as Riley's 



figure clearly shows. Leptus irritans is 

 the larva of a species of Trombidiidae, 

 but the characters given by Riley are not 

 even of generic value; hence it appears 

 that it will never be known certainly what 

 species his irritans is. 



In New Jersey, Maryland, the District 

 of Columbia, Virginia, and southeastern 

 Iowa there is apparently a single chigger 

 species. The writer has examined many 

 specimens from these sections and finds 

 that they are all the same. 



In the northern and western part of 

 the United States there is another very 

 closely related species which has the 

 body shaped exactly like the first men- 

 tioned but has more dorsal spines on the 

 abdomen, and fewer branches or barbs 

 on the palpal setse. This is the species 

 studied by C. W. Howard (6). Specimens have been examined from 

 Minnesota and Kansas. 



NOTES ON SEASONAL HISTORY. 



Chiggers are especially pests of the summer months, as has long 

 been known, but the period of their activity has not been known, 

 even relatively. During the year 1919, at Washington, D. C, the date 

 of the first record of larvae attaching themselves to man was July 2, 

 and by July 17 larvae were present in great abundance. On the 

 latter date the writer was severely attacked. During the remainder 

 of July and the whole of August the chigger larvse continued in 

 great abundance, and almost daily records of their attacks were 

 obtained. In September the attacks were much less severe, yet con- 

 tinued. On 'September 22 several larvse attached themselves to man 

 at Chesapeake Beach, Md. No records for the northern part of the 

 United States of chigger attacks in October have been brought to 



Fig. 1. — Dorsal view of an 

 American chigger (legs omit- 

 ted), X 150. This drawing 

 was made from specimens in 

 the University of Minnesota 

 collection, which were taken 

 at Lake Minnetonka, Minn. 



