BIOLOGY OF THE FLOWER 163 



stage in their life-cycle that insects lay their eggs. In time the 

 eggs are hatched, and the very small grubs or caterpillars have 

 to search for food with which to complete their development. 

 As they are mostly vegetable feeders, the caterpillars or larvae, 

 especially of moths and butterflies, do much damage to plants ; 

 and, if they are abundant, may strip a whole forest of its leaves 

 in a short time. Garden and field crops often suffer greatly from 

 this cause, resulting in a loss of many thousands of pounds. 



Insects of many kinds, either in their larval or adult stage, are 

 destructive to plants, both wild and cultivated. On the other 

 hand, some are useful. Among the more destructive are : 



Injurious insects. (1) The small Aphides or Plant Lice, and Scale 

 Insects (Hemiptera), which make great ravages in both garden 

 and field. 



(2) The larvae of butterflies and moths (Lepidoptera), e.g. the 

 Cabbage White Butterfly, the Cabbage Moth, Magpie Moth, and 

 Antler Moth, which injure field and garden crops. The Lackey 

 Moth, Buff-tip, Vapourer Moth, Ermine Moth, and several Tor- 

 trices affect fruit and forest trees. 



(3) The larvae of many flies (Diptera), such as the Wheat 

 Midge, Gout Fly, Daddy-long-legs or Crane Fly, Cabbage Fly, 

 Radish Fly, Mangold Fly, Onion Fly, and Root Fly are pests on 

 roots and other crops. 



(4) Larvae and mature beetles (Coleoptera) , especially the Mustard 

 Beetle and many Weevils. 



(5) Many Hymenoptera, such as the Gooseberry Saw-fly, Pine 

 Saw-fly, Turnip Saw-fly, and Corn Saw-fly, are often very destructive 

 to both herbaceous and woody plants. 



Fortunately for man, these pests are the chief source of food for 

 certain animals, and are thus kept in check. Such birds as the Fly- 

 Catcher, Wagtail, Tits, Wren, Hedge-Sparrow, Swallow, and others, 

 eat insects in enormous numbers. The Lady-bird Beetles, both larvae 

 and mature beetles, live on Aphides, Scale Insects, Mites, and other 

 pests, and are invaluable friends of the farmer and gardener. The 

 larvae of Ichneumon flies live as parasites within the bodies of 

 many plant-eating insects, and so destroy large numbers. It is 

 thus important that nature's balance should not be interfered 

 with. Man often destroys useful animals, and in consequence 

 suffers from the depredations of pests which these animals would 

 naturally keep in check. 



As botanists, our chief interest in insects is as pollinators 

 of flowers, and we will examine a number of common forms 



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