310 REPORT UNITED STATES ENTOMOLOGICAL COMMISSION. 



Dary observer the appearance of a bright red obloDg-ovoid body grow- 

 ing from the wing. They are so firmly attached by the mouth, so 

 immovable, and with the legs so short and hidden, that persons unfa- 

 miliar with their true nature might easily mistake them for some natural 

 growth or excrescence. That they are often so numerous as to weaken 

 and kill thieir victim, reports, as well as our own experience, clearly 

 prove. Professor Aughey, of Nebraska, has observed that these red 

 mites increase on the locusts immediately after a rain, and it is not im- 

 probable that they hatch more freely or move more freely in wet weather, 

 though the true explanation of the facts observed may also be found in 

 the repose of the locusts during such weather, and the greater ease with 

 which the mites consequently crawl upon them. They are most numer- 

 ous on the winged locusts, though also found upon the young, unfledged 

 insects, especially the pupse. 



In due time, these swollen bodies let go their hold and drop to the 

 ground, where, clumsily and with difficulty, they crawl under the first 

 shelter afforded by some bit of loose earth, or a stone. Here they re- 

 main quiet for two or three weeks, gradually swelling and changing form. 

 During this change, the pupa state is assumed, but not by shedding any 

 skin, as do true insects in going through their transformations. New 

 legs, feelers, and mouth-parts form under the old skin, which, with its 

 now useless legs, distends so as barely to cover the new parts, which are 

 all appressed to the body very much as in the pupa of a beetle (Fig. 40, 

 6). Finally both the distended larval skin and the new one that incases 

 the pupa burst, and release a creature quiet different from the former 

 Astoma — in fact, none other than the 8-legged TromUdium (Fig. 40, c). 

 We thus see that from the time this mite hatches, through all its growth 

 and changes, but one molt takes place. The mature form passes the 

 winter in the ground, and is active whenever the temperature is a few 

 degrees above freezing-point. 



Only two species of the genus Tromhidium have been described in 

 America, viz : scabrum Say, and sericeum Say.'^^ The descriptions in both 

 cases are brief, and lacking in structural details and in measurements. 

 The locust mite under consideration has been hitherto referred to seri- 

 ceum, but the characteristic polished anal plate precludes the reference, 

 and we define it under the name of locxistarum. Since the time when it 

 was established by Fabricius, evidently on the characters of the Euro- 

 pean T. holosericeiim, the genus Tromhidium has been greatly modified by 

 different authors. The species have been variously arranged according 

 to relative length of legs, position of eyes, divisions of the body, &c. 

 As restricted at present, the genus is thus characterized: Abdomen 

 swollen, especially in front, where it is broadest j cephalo-thorax small 

 and narrow, with two eyes, superior and barely raised ; legs T-jointed, 

 palpate, with two minute terminal hooks, the front pair longest, the 

 two front pairs widely separated from the two hind pairs ; mandibles un- 



" Joum. Ao. Nat. Sc. Phil, ii, 1821, p. 70. 



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