312 EEPORT UNITED STATES ENTOMOLOGICAL COMMISSION. 



apods in their early life, aud there can be no doubt but that all the 

 TromUdidce have hexapod larvae. In addition to the locust mite above 

 described, we have found another larval form attacking the mature G, 

 sprettis. It is at once distinguished from the larva of locustarum by the 

 more prominent head, by the longer, more slender legs, which 

 are 7-jointed, the joints increasing in length to the penultimate, 

 which is longest, and by the hairs, whether on the body, legs, 

 or palpi, being long, tapering, and barbed. It is possibly the 

 larva of a large species, which we have called Tromhidium 

 gigaiiteum, distinguished by the following characters : 



TROMBiDiu^r GiGANTEUM Eiley. — Adult 8 mm. to 9 mm. long; pyri- 

 form, somewhat flattened ; no pronounced constrictions, but various dorsal 

 irregularities; usually about five pairs of circular depressions connected 

 by transverse ones on anterior two-thirds, and a triangular series poste- 

 riorly. Barbed hairs long aud tapering, but very dense and even. Color 

 deep scarlet, the legs concolorous ; eyes dark. Characterized by the 

 penultimate palpal joint forming a single claw with a prominent notch, 

 Trombidium while the terminal thumb is large, extending one-third its length beyond 

 a^BedafciawT *^® claw, clavate, and with the inner side of its broad end flattened ; the 

 fti labial claw claw, as wtll as the thumb, having sparse hairs; terminal joint of legs 

 and thuTiib. squarely docked, with the claws reaching but little beyond the side. 

 (After Eiley.) Living in the ground. Nine specimens examined. 



We have also reared to the perfect state the well-known Astoma para- 

 site that attacks the common house-fly {Musca domestica) 

 in this country, and will add a description of it by way of 

 comparison, as it may also be found to attack locusts. 



The larva (Fig. 42) has the same mode of transformation 



as T. locustarum^ but is much more active after detachment, 



while the gradual shrinking and withdrawalof the larval 



legs during the transformation to pupa is much more easily 



observed. The species is distinguished from T, locustarum 



by the following characters: 



Trombidium muscakum Riley. — Larva distinguished from that of T, locustarum by the 

 greater relative length of legs, and by the hairs on the body being 

 much longer and more -conspicuous ; also by the more distinct 

 transverse sutures, of which there are four. Transverse striations 

 noticeable soon after attachment. Full-grown larva also more 

 active. 

 Pupa. — More rounded behind. 



Adult. — Average length 1.2 mm. ; color bright and pale scarlet ; 

 legs very pale and with the terminal joint fusiform and the claws 

 TiT^'^'^f.^SiJrT^^^^^io' much longer than in T. locustarum, and more nearly as found in the 

 bial claws and thumb; larva ; body rounded, very little narrower behmd, with no impres- 

 5, pedal claws ;c, barbed sions or other marks. Barbed hairs of body sparse, short, blunt, 

 tubeiculoushair. (Af- and tuberculous, giving a beautifully echinulate appearance under 

 ter Kiiey.) ^1^^ microscope. Genital depression circular ; penultimate jDalpal 



joint ending in two small, equal, blunt claws, the thumb being very small, tuberculous 

 .and not reaching its tip. No marked sexual differences. 

 Many specimens examined. 



The mode of growth of these mites may be more clearly illustrated by 

 n brief reference to a common red Tvater-mite {Hydrachna helostomce 

 IRiley) which we have studied. The mites of the typical genus Hydrachna 

 are, in reality, the aquatic representatives of Trombidium^ and have a 

 precisely similar mode of development. We have not had the eggs, 

 but in Europe they are known to be laid in spring in holes in soft- 

 .stemmed aquatic plants. 



FiG.42.— Larvaof 

 Trombidium mus- 

 cakum. (After 

 Kiley.) 



