Type of antsThe relation of ants to aphids is most interesting. It does not exist with all species of ants but in at least a large number honeydew is an important part of their diet and in some cases it may be their only food. There is every evidence that the benefit is mutual, the ants protecting the aphids, driving away the enemies of these insects or carrying the aphids to protected places. Ants that care for root-feeding aphids keep them in clambers or galleries, conduct them to their sources of food supply, collect and store their eggs for the winter and in spring take the young to their food.
The corn root aphid so injurious to corn, as already described, is thus cared for by ants. Scale insects which produce honeydew are also cared for in a sense, for ants are very attentive to them and to quite an extent prevent the attacks of the enemies of the scales by their presence and activities. Thus in an indirect way the protection by ants of aphids, scale insects, whiteflies, leafhoppers and in fact any insects which produce honeydew establishes such ants as injurious.
Some kinds of ants have most remarkable habits worthy of a brief reference here. Some species may make raids on the nests of other kinds and carry off their worker larvae and pupae to their own nests, where many probably serve as food but a few may be reared and become slaves. Slavery is not essential with all kinds of ants where it is known, colonies having no slaves being able to carry on their lives unaided by slaves. With certain species, however, the situation is different.
In these the workers have mandibles so constructed that they are unable to gather food, excavate their nests or care for the young. Accordingly, they make forays on the nests of other species, bringing back larvae and pupae which on becoming adult are slaves which do the work of the colony and care for their captors, both as adults and during their early stages.