HYMENOPTERA 379 



then cuts several circular pieces of leaves, the diameter of which is a 

 little greater than the diameter of the tube, and forces them into the 

 open end of it, thus making a tightly fitting plug; three of these circular 

 pieces have been cut from the spray figured. Usually several cells of this 

 kind are placed end to end in a burrow; and sometimes many bees will 

 build their nests near together in the same piece of wood. 



Family Bombid^e 

 The Bumblebees 



The family Bombidse includes the well-known nest-building bumble- 

 bees and certain parasitic bumblebees, Psithyrus, that infest the nests of 

 the nest-building species. The members of this family are large bees or 

 of medium 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 nest-building bumblebees, Bomb us. — The members of this genus 

 are social insects, each species consisting as in other social insects of three 

 castes, the queens, the workers, and the males. In this genus the queens 

 as well as the workers possess pollen-baskets or corbiculae 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, ex- 

 cept 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 peren- 

 nial, 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." 



Many observers have studied the founding and development of col- 

 onies of bumblebees; among these is Sladen who has made very detailed 

 studies of the species found in England. The following condensed sum- 

 mary 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 lump of paste made of pollen moistened with honey. 



