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Nature-Study Agriculture 



Ladybird 

 beetles 



Spiders 



Parasitic 

 insects 



How 



some of 

 them work 



turned loose in the orchards. They multiplied rapidly, 

 and soon the ravages of the cottony-cushion scale were 

 checked. Now if that pest is seen to be increasing in 

 any locality, ladybird beetles are brought from the 

 state insectary (where beneficial insects are reared 

 for the public), and they quickly control the pest. 



There are known to be two thousand kinds (species) 

 of ladybird beetles, most of which, both as larvae and 

 adults, live on other insects (are carnivorous) and are 

 helpful to men. Only two of the kinds that are known 

 in the United States, the squash ladybird and the bean 

 ladybird, are plant eaters (herbivorous) and therefore 

 pests. Plant lice, which do so much damage, form the 

 chief diet of one ladybug. Thousands of pounds of 

 these insects are annually collected in the mountains 

 where they breed and are sent to districts in which 

 they are needed for the control of plant lice. 



Spiders are of very great service in holding insects 

 in check. Strictly speaking, the spiders should not 

 be classed as insects : a true insect has three pairs of 

 legs ; a spider has four. 



There is another class of insects called " parasites," 

 many of which destroy pests, not by devouring them, 

 but by attacking them from within. The insect at- 

 tacked is known as the " host." Most commonly a 

 parasite lays its eggs in the body of an insect, piercing 

 the skin with a sharp egg-laying device called an " ovi- 

 positor." Then, when the eggs hatch, the grubs (larvae) 

 feed upon the body of the host, killing it. Sometimes 

 a small insect parasite pierces the eggs of a larger insect 

 with its ovipositor and lays its own tiny eggs within. 



