HYMENOPTERA 985 



are large bees or of mediiim size ; they are robust with oblong bodies 

 and a rather dense covering of hair. They are common, and are 

 conspicuous on account of their noisy flight and striking coloration, 

 which is usually yellow and black. They are called bumblebees on 

 account of the sound they make in flight; in England they are 

 commonly known as humblebees. 



The distinctive characters of this family are given in the table of 

 the Clistogastra on page 912. Most writers recognize only two 

 genera in the Bombidae, Bonibus and Psithyrus; but some have sepa- 

 rated certain species from Bonibus and placed them in a separate 

 genus, Bomhias. As there is considerable doubt regarding the validity 

 of this genus it will not be discussed here. 



The nest-building btmiblebees, Bonibus. — The members of this 

 genus are social insects, each species consisting as in other social in- 

 sects of three castes, the queens, the workers, and the males. In 

 this genus the queens as well as the workers possess pollen-baskets or 

 corbiculaj on the hind legs; as the queen when founding a colony 

 must collect pollen. 



With the bumblebees the queens are larger than either the workers 

 or the males and, in temperate regions, are the only ones that live 

 through the winter; as in these regions the colonies, like those of our 

 northern species of social wasps, break up in the autumn and all of 

 the bees, except the young queens perish. These crawl away into 

 some protected place and pass the winter. In the spring each queen 

 that has survived the winter founds a new colony, performing, until 

 a brood of workers has been developed, both the duties of queen and 

 of worker. In South America, where according to von Ihering, 

 bumblebee colonies are perennial, new nests are formed by swarming 

 as among the social wasps of the same region. 



In selecting a place for her nest the queen usually chooses a 

 deserted mouse-nest, within which she builds her nest; sometimes an 

 old bird's nest is used for this purpose. In certain European species 

 the queen, sometimes at least, constructs her nest entirely without 

 making use of a nest of another animal. This she does by making 

 use of moss or soft dead grass, which she combs together with her 

 mandibles and legs, for this reason these species are often known as 

 "carder-bees." 



IVIany observers have studied the founding and development of 

 colonies of bumblebees; among these is Sladen ('12) who has made 

 ver\' detailed studies of the species found in England. The following 

 condensed summary is based on the statements of this author. 



Having found a suitable nest the queen spends a good deal of 

 time in it, the heat of her body gradually making its interior perfectly 

 dry. She then gathers the finest and softest material she can find into 

 a heap and in the center of this makes a cavity with an entrance at 

 the side just large enough for her to pass in and out. In the center of 

 the floor of this cavity she forms a linnp of paste made of pollen 

 moistened with honey. Upon the top of this lump she builds with her 

 jaws a circular wall of wax, and in the little cell so formed she lays 



