150 PROCEEDINGS OF THE NATIONAL MUSEITM vOL. 106 



Evidence indicates that E. peromysci is a forest soil dweller 

 in the Duke Forest area. All collections of the unattached, un- 

 engorged chiggers have been from forest soil situations (table 5). 

 Whether its principal host, Peromysciis leucopus, is a soil dweller 

 in Duke Forest has not been proved, but circumstantial evidence 

 from the traplines — the frequency with which it was trapped 

 around decayed stumps, at the bases of fallen trees, and at small 

 holes in the forest floor — indicates that it is. 



Collection records show that E. peromysci has been most abun- 

 dant during the coldest seasons of the year. Figure 6,c, con- 

 stiiicted from the occurrence of the chiggers in collections, re- 

 flects the trend of seasonal populations. Hov/ever, three chiggers 

 on one host in a June collection influenced the graph as much as 

 perhaps fifty chiggers on every host of a January collection. The 

 result has been a much-flattened graph without the amplitude 

 that it would have had if based on counts of the chiggers. 



Results of preliminary investigations into factors controling 

 seasonal distribution of E. peromysci indicate that it had its peak 

 population during the season when temperatures of air, surface 

 soil, and subsoil (three inches depth) were lowest (fig. 6,e). 



Explanation of figure 5 



a. Variation geographically in the size of scutum in 100 specimens of Euschongastia 

 ■peromysci. Vertical axis: Size of scutum, PW + ASB + PSB (width + length), 

 in microns. The means are indicated by crosslines. Horizontal axis: Counties, with 

 the number of scuta measured for each: A, Rowan County, Ky.; B, Orange County, 

 N. C; C, Durham County, N. C; D, Clermont County, Ohio; E, York County, Pa.; 

 F, Cameron County, Pa.; G, Prince Georges County, Md.; H, Bradford County, Pa.; 

 I, Sullivan County, Pa.; J, Monroe County, Pa.; K, Westmoreland County, Pa.; L, 

 Lancaster County, Pa.; M, Lycoming County, Pa.; N, Union County, Pa.; P, Jefferson 

 County, Pa.; Q, Schuylkill County, Pa.; R, Bedford County, Pa.; S, Clearfield County, 

 Pa.; T, McKean County, Pa.; U, Venango County, Pa.; V, Wayne County, Pa.; W, 

 Indiana County, Pa.; X, Center County, Pa.; Y, Beaver County, Pa.; Z, Pike County, 

 Pa. 



b. Variation geographically in the length of 70 palpal claws of Euschongastia peromysci. 

 Vertical axis: Length of the claws in microns. The means are indicated by crosslines. 

 Horizontal axis: Counties with the number of separate palpal claws measured from 

 each: A, Clermont County, Ohio; B, Rowan County, Ky.; C, York County, Pa.; 

 D, Lancaster County, Pa.; E, Durham County, N. C; F, Orange County, N. C; G, 

 Westmoreland County, Pa.; H, Union County, Pa.; I, Lycoming Countj', Pa.; J, 

 Cameron County, Pa.; K, Bedford County, Pa.; L, Jefferson County, Pa.; M, Venango 

 County, Pa.; N, Clearfield County, Pa.; P, McKean County, Pa.; Q, Sullivan County, 

 Pa.; R, Monroe County, Pa. 



c. Variation geographically in the size of scutum of 20 specimens of Euschongastia di- 

 versa diversa. Vertical axis represents size of scutum, PW + ASB + PSB (width + 

 length), in microns. Horizontal axis: A, Clarke County, Iowa; B, Clermont County, 

 Ohio; C, Scioto County, Ohio; D, Union County, Pa. Five scuta were measured for 

 each county. The means are indicated by crosslines. 



