HABITS OF THRIPS. 145 



doing essential injury to plants. But seasons sometimes 

 occur, when their increase is so prodigious that severe 

 damage ensues, both to the crops of the husbandman, 

 and to vegetation generally. Among the hop plant- 

 ations, for instance, the Aphides are so prevalent, that 

 the scarcity or abundance of the crop entirely depends 

 upon their ordinary prevalence or unusual plenty ; and 

 hence the frequent reports on this subject in the news- 

 papers. Vain would be the attempt to clear a hop 

 garden of these pernicious insects, or to rescue any ex- 

 tensive crop from their baneful ravages. Even violent 

 rain has but a partial effect in destroying them. Mr. 

 Curtis immersed, in a glass of water, the footstalk of a 

 leaf of considerable length, from a stove plant beset 

 with Aphides. On immersion, they did not quit the 

 stalk, but immediately their bodies assumed a kind of 

 luminous appearance, from the minute bubbles of air 

 which issued from them. After an immersion of six- 

 teen hours, they were taken out and placed in the sun- 

 shine, when some of them almost immediately showed 

 signs of life, and, upon an average, not one out of four 

 was killed. So little effect, indeed, had this cold bath 

 upon the rest, that one out of the survivors, a male, 

 very soon after became winged, and another, a female, 

 was delivered of a young one ! 



(135.) The Thripsoi Linnaeus are such exceedingly 

 minute insects, that to the naked eye they seem but as 

 little specks, or rather like short lines, not exceeding 

 the length and thickness of the letter i. In spring, these 

 minute creatures may be found running about the petals 

 of flowers, particularly the dandelion ; but in summer 

 and autumn, they fly into houses, if not in swarms, at 

 least in considerable numbers ; they alight upon the 

 hands and face, and occasion that troublesome irritation 

 which many people experience during hot weather, 

 without knowing the cause. Minute as these creatures 

 are, Mr. Kirby considers them as highly noxious to the 

 farmer, by deriving their nourishment from the embryo 

 grains of the wheat plant. 



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