THE SOCIAL INSECTS 



some species, however, the queens have been known to pair 

 with a brother, in or near the nest. 



In most species queen and worker humble bees differ very- 

 little from one another except in size. In the larger, subter- 

 ranean species the gap in size between the two castes is 

 appreciable and there is almost no overlap. In the carder 

 bees, however, the two types almost run into one another, 

 probably because this group of humble bees has not evolved 

 so far as have the others. 



A study of the differences between workers and queens 

 has been made by the author and by R. A. Cumber. A 

 picture of this type of investigation will be obtained if a nest 

 is described which was excavated at Silwood Park, Berks, on 

 July 4, 195 1, by Dr. N. Waloff and myself. It was a nest of 

 Bombus hortorum, about six inches underground, in an old 

 mouse-run in a hay field. The bees were divided into three 

 lots : first, those that were out foraging and returned to the 

 nest while it was being excavated, mostly carrying pollen 

 on their hind legs ; second, those that came out to defend the 

 nest while it was being dug out ; third, those that stayed on 

 the comb and were removed from it, one by one, in the 

 laboratory. The weights of these three lots of bees and their 

 status in the nest are shown in the table opposite. Although 

 there is some overlap, the average difference in weight of the 

 three lots of workers is very striking. The old queen 

 (weight 553) was recognisable by her rather battered appear- 

 ance. Only one of the other queens (weight 442) had been 

 fertilised, as was shown later by dissection. The colony was 

 a rather small one and it may be for this reason that one of the 

 young queens was carrying a load of pollen. Besides these 

 bees, the nest contained six eggs, twenty-four grubs, sixty- 

 six full cocoons, fifty-one vacated cocoons containing honey, 

 and one cell containing pollen. There were also twenty-six 



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