The "aculeate", or stinging, Hymenoptera, are divided into sections and families according to their structure; but the groups which stand out most clearly in regard to their habits are the solitary and social species, the predaceous and non-predaceous and the inquilines or cuckoos.
The vast majority of the aculeate Hymenoptera are what are called "solitary", i.e. one male and one female alone are interested in the production of the nest; but there are also three "social" groups—the ants, the true wasps, and the humble and hive bees.
These are called social because they form communities and all work together towards the maintenance of the nest. In the social species there are two forms of the females—the queens and the workers; these latter have the ovaries imperfectly developed, and in the humble bees and wasps they only differ outwardly from the fully developed females or queens by being smaller. In the ants, however, the workers are wingless, and of a very different form from that of the queen. The rôle of these workers seems to be to do the general work of the nest; they have been known to lay fertile eggs, but the resulting offspring has always been male.
Between these conditions of solitary and social we know of no actually intermediate stages. We do not seem to see any attempts on the part of solitary bees to become social or vice versâ. The only condition known which
could possibly be considered as intermediate is shown in certain species where a number of individuals make their nests close to each other in some particular bank, forming a colony. These colonies are sometimes very extensive, and the burrows of the individual bees very close together; it has also been shown that the burrows sometimes unite—at the same time there seems to be no positive evidence that there is any work done in the colony which could be considered as done for the common good.
THE SOLITARY GROUPS
All the solitary kinds appear to feed themselves on vegetable juices, honey, etc., but there is a well-marked division between those who provision the cells of their offspring with insects, either fully developed or in the larval stages, and those who provision them with the pollen of flowers, honey, etc. The theory is that originally all fed their cells with insects, but that by degrees the more progressive found that the food which suited themselves would equally nourish their offspring, and accordingly provided them with vegetable nourishment. We find no intermediate stages. A certain class still goes on feeding on the old principle. The members of this class are known as "fossors" or diggers, while those which feed on the new principle are called "Anthophila" or flower-lovers. These are not very happy names, as many of the Anthophila dig out holes for their nests just