10 ANIMAL LIFE AND HUMAN PROGRESS 



wasps. They belong in part to a family known as the Chalcidae, 

 which are characteristic parasites of other insects, laying their 

 eggs in the bodies of their victims at various stages of their 

 life-history. The chalcids are very wonderful creatures, ex- 

 hibiting the most marvellous instincts in the selection of the 

 appropriate places in which to deposit their eggs. Those which 

 occur in grain feed upon the larvae of the beetles, but very little 

 is known about them and this is a field of research which it is 

 hoped will be explored in the near future. The fact that over 

 5000 species of chalcid parasites have already been described 

 from various sources may serve to give some idea of the 

 enormous extent of the ground that has to be covered by 

 zoological investigation. 



Nor are these the only insects that occur in stored cereals, 

 for various small moths and their larvae frequently make their 

 appearance, and genuine bugs are occasionally met with. 

 Little is known of the latter, but they probably feed as parasites 

 upon the larvae of other forms. As a matter of fact, even the 

 notorious bed-bug appears to be really a very well-meaning 

 little creature from the human point of view, and it is only 

 quite by accident that it makes itself objectionable to mankind. 

 It finds its natural food in the larvae of the boring beetles which 

 infest old furniture, with which it is said to have been intro- 

 duced into this country in the reign of Queen Elizabeth. 



In addition to the true insects badly infested samples of 

 grain may also contain enormous numbers of microscopic 

 mites. Some of these closely resemble the common cheese- 

 mite, while others are very curious little creatures which 

 again live as parasites upon the larvae of the grain-insects. 



If you wish to gain the upper hand in dealing with your 

 enemy it is always advisable to get to know as much about 

 him and his habits as possible, for you never know where a 

 weak spot in his defences may reveal itself. A problem like 

 that of the grain-pests has to be studied from every point of 

 view in the hope of finding a remedy. We want to know all 

 about the life-histories of the insects we are attacking in order 

 to ascertain whether any one stage is more vulnerable than 

 another, and at what period it is most desirable to apply 



