242 TRANSFORMATIONS OF INSECTS. 
are either permanent or only last a year. The solitary species 
lead a life like that of the fossorial Hymenoptera; and a single 
female constructs a nest, makes the cells for its larve, and 
victuals them. The social bees have three kinds of individuals— 
namely, males, fertile females, and neuters, which are also called 
workers or sterile females. In those colonies which only last a 
year some solitary female lays the foundation of the hive, and the 
workers are gradually born and increase in number; but the 
fertile females which are found in permanent colonies never do 
any work, and, indeed, they are incapable of it, for the neces- 
sary structures are wanting inthem. There are certain species 
amongst the bees—whose habits are like those of some insects 
which have already been noticed in treating of the Sphegide— 
which have the instinct to enter the nests of industrious kinds, 
and to deposit their eggs in the cells that have been partly filled 
with food intended for the larve. 
The bees we shall first notice differ from all others by not having 
their hind legs made to collect pollen, and the genus Osmza con- 
tains the most important of them. These ymenoptera build very 
elaborate structures, and take almost a fantastic care about the dif- 
ferent materials which they use for their cells, each species choosing 
particular substances. They collect pollen, like other nest-making 
Hymenoptera, and make a cake of it for their larve, but their legs 
do not assist them in collecting it. But there are some stiff and 
crowded hairs which cover the lower part of the abdomen of 
these bees, and they answer the purpose of pollen collectors just 
as well as the hind legs of the other bees. The Osmia rubs itself 
against the stamens of flowers, and detaches the pollen, then it 
collects some grains against the hairy structure, which retains 
them, and then the insect returns to its nest carrying a greater 
or less quantity of this important food. Of course the first care 
of the bee should be to get rid of its burden, but it does not 
appear, at first sight, how this sticky pollen is to be moved 
from off the hairs; but a structure is at hand by which this diffi- 
culty can be overcome at once, for the Osmza is provided with a 
kind of brush, which is placed under the first joint of the hind 
legs, and as these extremities can be moved in all directions, 
every morsel of pollen is speedily detached from the whole body. 
