OBNOXIOUS INVERTEBRATES. 357 



tances. The light of the sun is darkened as they pass, 

 and the air is filled with a dull sound, caused by the 

 striking of their wings. At last, carried by the wind, 

 they fall like a rain-storm ; trees are stripped of leaves, 

 and the branches break under the weight of the insects ; 

 all vegetable life disappears ; harvests are devoured. 

 Then, to complete the desolation, the bodies of the in- 

 sects that are crushed in the mass, exhausted by hunger 

 or by fatigue, form on the naked ground a thick layer 

 of decomposing matter that serves as a hot-bed of dis- 

 ease. Eussia, Poland, and Hungary have been several 

 times plague-stricken from this cause. 



The phylloxera lives as a parasite on the roots of the 

 grape-vine, and increases with frightful rapidity. It is 

 rendered still more destructive by the fact that, be- 

 sides the apterous individuals that remain fixed on the 

 roots, there is a winged form that carries the pest in all 

 directions. The winged insect lives on the leaves, and 

 lays eggs that produce apterous individuals. The latter 

 penetrate under the skin of the root, and by their suck- 

 ing apparatus kill the vine by pumping all the juices of 

 the plant. 



During the warm season the apterous individuals 

 produce, by a sort of budding, large numbers of young, 

 among which some develop into winged insects. The 

 latter migrate, and, as we have seen, lay eggs, from 

 which wingless and less injurious individuals are hatched, 

 but from these are produced the destructive and the 

 winged forms. 



The termites, or white ants, are of many species ; they 

 have multiplied to such an extent in certain towns of 

 France that attempts to destroy them have proved 

 almost useless. At La Eochelle they invaded the public 



