418 FLEAS 



It is said to be very annoying to man also. The common squir- 

 rel flea in North America, C. acutus, is found on a number of 

 species of wild rodents, and also occasionally on rats and mice. 

 It does not attack man so readily as does C. fasdatus, but is 

 nevertheless not averse to human l)lood. This species has 

 come into great importance in California as the transmitter of 

 plague from rats to ground scjuirrels. It is probable, how- 

 ever, that other species of this genus and of allied genera 

 may quite as readily transmit plague, depending only on the 

 extent to which their habits bring them in contact with infected 

 animals. 



Chiggers. — The chigger, chigoe, jigger or sand flea, Derma- 

 tophilus (or Rhynchoprion) penetrans (Fig. 183), as it is vari- 

 ously called, is one of the most de- 

 spised pests of tropical countries. 

 It is a very small flea of the family 

 Sarcopsyllidae, about one mm. in 

 length, with no comblike spines 

 and relatively slender legs. It has 

 a very comical pointed forehead, 

 like a helmet worn with the point 

 forward. The males and virgin 

 females of this species are similar 



Fu;. 183. Chigger or burrowing , .in • i i -j. j. ^.i j. 



flea. Dermatophilus penetrans, un- ^O Other flcaS m hablts, eXCCpt that 



irapregated female. X 30. (After they attack a widc range of hosts. 



Karsten from Riley and Johannsen.) -.^ • ,i •• i, , <>.i- 



Man IS the prmcipal host of this 

 particular species, but pigs are also very commonly attacked. 

 Chiggers occur especially in sandy regions where there is much 

 underbrush, and here they lie in ambush on the vegetation, dead 

 leaves or sandy soil, ready to attack any host which may come 

 their way. The particular importance of this flea lies in the 

 fact that the impregnated females have the aggravating habit 

 of burrowing into the skin especially in such tender spots as under 

 the toe nails, where, nourished ]jy the blood of the host, the eggs 

 develop and cause the abdomen to swell into a great round ball 

 as large as a pea, leaving the head and legs as inconspicuous 

 appendages (Fig. 184). Only the two posterior segments of the 

 abdomen do not enlarge; these act as a plug for the hole made in 

 entering the skin. The eggs, up to a hundred in number, mature 

 in about a week and are then expelled by the female through the 



