84 



REPORT 108; U. S. DEPAETMEXT OF AGRICULTURE. 



Fig. 164.— Parasitus predator. 

 Leg II of male. (Original.) 



Parasitids of various kinds occur on the seacoasts, and often have the caronclee 

 modified or enlarged and adapted to the moist soil. Several new genera have been 

 based on such forms as Cyrthydrolaelaps, which is a Cyrtolaelaps , except the peculiar 

 foot. Most of these maritime forms have evidently been developed independently 

 from the adjacent parasitid fauna, and exhibit convergence in structure. Very 

 similar forms are known from the coasts of Europe and from 

 certain Antarctic islands. 



The genus Podocinum is remarkable on account of the 

 very long front legs, which the mite uses as feelers. The 

 species occur under sticks on moist ground; one of our 

 species is very common. The species of Paragrccnia (fig. 

 158) {Greenia Ouds. and Greeniella Bks., both preoccupied) 

 are remarkable for inhabiting a ca\dty in the basal abdomi- 

 nal segment of certain female bees of the genus Koptortho- 

 soma. With them have been found other mites, especially 

 of the genus Trichotarsus. The relation of the mites to the 

 bees is not fully known ; the basal segment of these bees is 

 strongly concave and its edges applied closely to the tip of 

 the thorax, thus forming a cavity with an opening above. 

 Within this cavity the Paragreenia occur, often nearly filUng it. These mites have 

 the front legs provided with short retrorse spines; several species have been described, 

 all from the Old World. In the female of an American species of Odynerus a similar 

 cavity is found where the apical margin of the basal segment rests on the front of the 

 nonconstricted part of the segment; a simi- 

 lar but und escribed genus of mites occurs in 

 this cavity. 



Anystipalpus is in general similar toLaelaps 

 but with the palpus formed on the manner 

 of theTrombidiidae, the last joint forming a 

 "thumb." 



Of Myrmozercon (including Myrmonyssus) 

 a large number of species have been de- 

 scribed, mostly from southern Europe. They 

 are found attached to the bodies of various 

 species of ants, and doubtless feed upon 

 them. They have short, stout legs with 

 very large ambulacra. 



A number of species of Laelaps occur on 

 small mammals and in their nests; thus L. 

 multispinosus Banks occurs on the muskrat, 

 L. pcdalis Banks on the chipmunk, L. pro- 

 pheticus Banks on the groundhog, and L. 

 echidninus Berlese on rats. They are sup- 

 posed to suck the blood of their hosts, but 

 may feed to some extent on the dennal 

 scales. L. echidninus Berlese (fig. 159) is a 

 very bristly form; it is found on rats in all 

 parts of the world, but probably has little to do with the transmission of any 

 human disease. Two other species have also been recorded from rats. Unlike the 

 ticks, these mammal-inhal)iting mites rarely if ever attack man or the domestic 

 animals, so that they are of little economic importance. But as vectors of plague 

 from rat to rat they are factors that must be considered in the eradication of that 

 dread disease. According to recent researches, Laelaps cchidnimis also carries a disease 



Fig. lijo.—Hyktast(s sp. and anal plate. 

 (Author's illustralion.) 



