HYMENOPTERA 



981 



about 6 mm. in length, and of a metallic blue color. She always selects 

 a twig with a soft pith which she excavates with her 

 mandibles, and so makes a long tunnel. Then she 

 gathers pollen and nectar and puts it in the bottom 

 of the nest, Idivs, an egg on it, and then makes a parti- 

 tion out of pith-chips, which serves as a roof to this 

 cell and a floor to the one above it. This process she 

 repeats until the tunnel is nearly full (Fig. 1123), then 

 she rests in the space above the last cell, and waits for her 

 young to grow up. The lower one hatches first; and 

 after it has attained its growth, it tears down the 

 partition above it, and then waits patiently for the 

 one above to do the same. Finally after the last one 

 in the top cell has matured, the mother leads forth 

 her full-fledged family in a flight in the sunshine. After 

 the last of the brood has emerged from its cell, the 

 substance of which the partitions were made, and which 

 has been forced to the bottom of the nest by the young 

 bees when making their escape, is cleaned out by the 

 family, the old bee and the young ones all working 

 together. Then the nest is used again by one of the 

 bees. ' I have collected hundreds of these nests and by 

 opening different nests at different seasons, have gained 

 an idea of what goes on in a single nest. There are 

 two broods each year. The mature bees of the fall 

 brood winter in the nests. 



Fig. 1223.— 

 Nest of Cer- 

 atina dupla. 



The large carpenter-bee, Xylocopavirgmica. — This is a large insect, 

 measuring from 22 to 24 mm. in length and resembling a bumblebee 

 in size, and somewhat in appearance. But it can be easily distin- 

 guished from a bumblebee, as the female has a dense brush of hairs 

 on the hind leg, instead of a basket for carrying pollen. This bee 

 builds its nest in solid wood, and sometimes excavates a tunnel a 

 foot in length, which it divides into several cells. The partitions 

 between the cells are made of chips of wood, securely cemented 

 together, and arranged in a closely-wound spiral. This arrangement 

 of chips is easily seen when the lower side of a partition is examined ; 

 but the upper side of a partition which forms the floor of the cell above 

 it is made concave and very smooth, so that the arrangement of the 

 chips is not visible. The nest of Monohia quadridens described on an 

 earlier page (Fig. 11 88) was probably made in a deserted tunnel of 

 Xylocopa. Mono6m, however, makes the partitions of its nest of mud. 



This species is distributed generally throughout the United States 

 and is the only species of Xylocopa found in the Northeastern part 

 of this country. Eight other species have been described from the 

 South and the West. A monograph of the species of Xylocopa of the 

 United States was published by Ackerman ('16). 



