112 SEVENTEENTH Report STATE ENTOMOLOGIST OF MINNESoTA—1918 
BB. No chitinous plates on the abdomen. 
(C. Tarsi I very much swollen, a very small species. 
Microtrombidium magnitarse 
CC. Tarsi I not so large; larger species. 
ID): White markings on the abdomen, eyes sessile, body 
hairs very slender. Microtrombidium albovittatum 
DD. No white markings on abdomen, body hairs not so 
slender. 
E. Body hairs spindle shaped, grooves on dorsum 
form an inverted triangle. 
Microtrombidium triangulum 
EE. Body hairs stout, with expanded tips or globose; 
no constriction of abdomen. 
Ee Hairs of body globose mixed with stout 
hairs whose expanded tips are turned 
backward. 
Microtrombidium nopal-rubrum 
FF. Hairs stout and thick, or with expanded 
tips turned backward; six pairs of large 
pits on the dorsum. 
Microtrombidium punctatum 
KEY TO) WARVAE 
IX Palpi with two claws, one simple and one bifurcate. 
B. Larger claw deeply bifurcate; spines on coxae slender and barbed; 
processes on mandibular sheath clavate with numerous spines on 
the tip. Allothrombium pulvinus 
BB. Larger claw not so deeply bifurcate, spines on coxae short and 
bifurcate ; processes on mandibular sheath clavate. 
Eutrombidium locustarum 
AA. Palpi with one bifurcate claw. 
B. Claws on third tarsi of equal length; processes on mandibular 
sheath blade-like or palmate. 
(CG Anterior dorsal shield long and narrow, lateral edges curled 
under posterior dorsal shield quadrate in outline; processes 
on mandibular sheath blade-like. 
Microtrombidium triangulum 
CC. Anterior dorsal shield as wide as long; lateral edges not 
curled under; posterior dorsal shield spindle-shaped ; processes 
on mandibular sheath palmate. 
Microtrombidium muscarum (?) 
BB. Claws on third tarsi not of equal length, the shorter one extends 
dorsad; processes on mandibular sheath brush-like. 
Sericothrombium scabrum 
Allothrombium pulvinus Ewing. 
All. pulvinus Ewing (in manuscript) 
Adult females: Color: dull scarlet, darker than Eu. locustarum, 
more nearly approaching Brazil red in tone, a small triangular area at 
