734 REPORT UNITED STATES GEOLOGICAL SURVEY. 



I append the following account of several potato-insects of Europe, 

 taken from Curtis's Farm Insects, and which may prove of interest, since 

 the same or closely-allied species are likely to occur in the United 

 States : 



"Dead and silent as the earth appears to be, it teems with life ; for not 

 only is the soil full of seeds, which merely require ligtit and heat to 

 start them into life, but it must abound with the eggs of insects so mi- 

 nute that even with the assistance of a lens they escape one's notice. To 

 be convinced of the truth of this, if a flower-pot be filled with mold 

 from a field or garden, and then tied over with the finest muslin, the 

 experimentalist will be astonished to find the multitudes of little flies 

 which are constantly making their appearance, bred no doubt from larv.ne, 

 nourished on the vegetable matter which such soils contain. Where 

 crops are grown, and any portion of them become decayed, the num- 

 ber of these minute insects is vastly multiplied, and thus where the 

 deceased potatoes have existed additional swarms of various little flies 

 have been the consequence. As a proof of the incredible numbers that 

 must be thus generated, I may mention that from one growing and par- 

 tially-rotten potato I bred in August, 1845, 128 flies, independent of 

 many more which had died in the pu[)a state, or been destroyed by damp 

 and mites before I discovered them in the vessel in which the tuber was 

 placed, as well as multitudes of smaller flies, all of which I will now 

 describe. 



"The whole belong to the order Diptera. The first I shall notice is 

 included in the family Tipulid^ and the genus Psychocla and has 

 been named — 



" P. nervosa. — The males are twice as large as the females ; they are ashy-white, 

 clothed with loiigish wool ; the little head is buried under the thorax ; the black eyes 

 are large and lnuat;e ; the two horns are as long as the thorax, and composed of eleven (?) 

 small points, black at the base, giving them an annulated appearance ; the abdomen 

 18 short, and of a dirty color ; the two wings when at rest meet over the back slant- 

 ing; they are iridescent, very large, oval, and lanceolate, with numerous longitudinal, 

 hairy nervures ; the entire margin is also hairy ; balancers small, clubbed, and white ; 

 six legs woolly ; the feet fine-pointed, the tips black ; length, f line ; expanse, 3 lines. 



"In February, 184G, the larvse and pupte were abundant in the rotten 

 potatoes, also in decaying leaves and dung-hills, and the flies have been 

 bred by Mr. Haliday from putrescent fungi. These flies sometimes 

 swarm in out-houses and about drains in spring and autumn. 



"The larvai are not ^ line long, yellowish-white, cylindrical, spindle- 

 shaped, with eleven distinct annulations besides the head, which is 

 triangular ; the tail is elongated and tubular. The pupa is about § line 

 long, ocherous, and ferruginous ; it is elongate-ovate in repose, but the 

 body can be stretched out and attenuated when disturbed; from the fore- 

 head project two slender appendages, like horns ; on either side are laid 

 the short, stout antennai, and the wings meet over the breast, with the 

 legs stretched out between them ; the abdominal segments are ciliated 

 and the tail is forked. 



"Several species of a little swarthy two- winged fly were bred from the 

 decaying potatoes in multitudes. They are called Sciara by Meigen 

 and Molohrus by Latreille. The larvai I received from Mr. Graham ; 

 they are slender worms, about \ inch long, whitish, and opaque, but 

 when immersed in water they become perfectly transparent, exhibiting 

 the ocherous viscera and the food digesting in the stomach ; when in 

 motion they taper toward the head, which is oval, horny, black, and 

 shining; the body is composed of thirteen segments, with seven or 

 eight spiracles on each side; the tail is broad and rounded, but slightly 

 pointed in the center. The pupa is shorter, cylindrical, elliptical, and of 



