THE SOCIAL INSECTS 



However, the red clover is a much more important flower 

 to man and has been much more studied. Clovers make a 

 rich fodder-crop and their roots bear nodules in which 

 bacteria multiply and convert nitrogen into nitrates. This 

 means that besides producing good food for cattle, the clover 

 also enriches the soil it grows in. Some clovers, such as the 

 common white species, have relatively short nectaries and 

 can easily be fertilised by the honey bee. The red clover, 

 however, which for some purposes is particularly valuable, 

 has a larger flower and is rarely fertilised by anything other 

 than one of the long-tongued humble bees. This creates a 

 difficulty whenever large fields of clover are grown for seed, 

 since there are rarely enough of the right kind of bee to 

 fertilise all the flowers. 



The problem has been studied in Britain at Aberystwyth, 

 in Scandinavia, in Russia, and elsewhere. It was proposed at 

 one time in Russia that wild humble bees should be 

 encouraged by the provision of large numbers of nesting- 

 boxes. For the shortage of bees is partly due to the absence 

 of sufficient nesting-sites, and this may in turn depend on a 

 shortage of mice. For other reasons, too many field mice 

 would be undesirable, so that it was thought that nesting- 

 boxes might be a substitute for abandoned mouse-nests. 



Probably the only practical measure is to grow the clover 

 in small patches rather than in the large continuous areas 

 which are much more convenient to the farmer. The prob- 

 lem arose in its most acute form in New Zealand, where 

 there are no native humble bees. For many years the red 

 clover set no seed, but in about 1880 bees were introduced 

 from England. Unfortunately, the introduction was not 

 carefully planned and besides one useful, long-tongued bee, 

 a short-tongued species was brought over at the same time. 

 Some of these short-tongued humble bees have the habit of 



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