LIFE-HISTORY OF THE LOCUST MITE. 311 



guiculate ; palpi large, free, the penultimate joint strongly ungulate, and 

 the terminal joint forming a movable thumb upon it. Larva 6-legged, 

 parasitic ; defined under the generic names Astoma, Leptus, Lepostomus^ 

 and Ocypete. Many species have been described in Europe, but the one 

 in question differs from all of them as given by Gervais."^^ 



Trombidium locustarum Riley. — Egg 0.12™°^ in diameter, spherical, full of gran- 

 ulatious, pale oraDge-red in color, becoming more pointed at one end before hatching 

 (Fig. 39, d), the shell splitting across and the severed sides rolling toward each other 

 when vacated (Fig. 39, e). 



Larva. — When newly hatched, x>ale orange-red, 0.14°^™ long, ovoid, the body with 

 but three transverse sutures, one anteriorly, one between first and second, and another 

 between second and third pair of legs ; dorsum with several transverse rows of about 

 six piliferous points; head somewhat narrowed, showing four minute swellings, each 

 giving rise to a rather long hair ; mouth-parts small and indistinct, with a dusky, 

 granular spot at their base; legs G-jointed, inclusive of fixed coxal piece, the third 

 joint longest, hind pair somewhat longer than the others, all tipped with two well- 

 developed claws, those on front pair the longest ; what appears to be a rudimentary 

 subcutaneous fourth pair; no anal setse. 



Full-grown larva. — 1.6°^°^ long, with the whole body greatly distended and elongated, 

 the elongation being j)rincipally from the posterior dorsal portion, so as to bring to 

 view four hairs at the end; body showing two principal transverse constrictions, one 

 about the middle, the other above it, while the whole surface is finely and trans- 

 versely striate 



Pu2)a. — 17"^™ long, one-half as broad. Either pale yellow or orange-red, polished, 

 swollen and rounded anteriorly, more tapering posteriorly, the dorsum well arched ; 

 two transverse impressions, at first noticeable but subsequently obliterated ; palpi 

 and legs formed under the larval skin, their ends finally projecting from it and more 

 or less free ; traces of the shriveled larval legs widely separated. 



Adult. — When first from pupa the color is orange-red, with a distinct transverse con- 

 striction about the middle, and a deep transverse impression in the broad fore part. 

 The species is characterized by the palpal claw consisting of one large hook, with a 

 second smaller one originating from its middle, and three stout spines from near its 

 base, and by the thumb being of uniform diameter, armed with rather long hairs ter- 

 minally, and reaching to or very little beyond its tip ; also by a sunken polished plate 

 at the end of the body dorsally ; the plate but sparsely covered with hairs, elongate, 

 square in front and broadening behind. The legs have the terminal hooks very short 

 and blunt, the front pair is longest, the second shortest. Hairs of body barbed, 

 slightly curved and attenuated. The scissor-like mandibles are faintly toothed within. 

 With age the color intensifies to scarlet, but the legs, palpi, and ventral surface are 

 always more pale and silvery than the superior part of the body. The male is smaller 

 than the female, has more intense color, relatively somewhat longer legs, with the 

 body more pointed behind and more deeply constricted ; the anal plate more narrow ; 

 ventrally his body is more distinctly constricted toward tip, and more deeply impressed 

 longitudinally ; also with the genital impression more distinct. His body becomes 

 more creased and impressed with age, while that of the female becomes broader and 

 more smooth and swollen. Average length of female when full-grown about 3 milli- 

 meters ; male abont 2 millimeters. 



W de-spread. We have it from Manitoba, Texas, various Eastern States, and from 

 California. 



In all the egg-masses we have examined, the number of eggs ranged 

 between 300 and 400, the mass being irregularly globose, and the eggs 

 but loosely adhering to each other. We have not been able to ascertain 

 the exact length of time required for the full development of the larva 

 after attachment, but it is brief, and seldom exceeds a fortnight, while 

 the final transformation, after detachment, occupies but three or four 

 days. Though the motion of the swollen and detpched larva is slow, 

 the legs move about with considerable rapidity; yet in the gradual 

 change to pupa they shrink and are partially drawn in. Since De 

 Geer's time it has been known that some of the octopod mites are hex- 



" Suites k BaflFon. Apteres. 1844. 



