HONEY MAKERS AND PLANT STINGERS
A long shelf is required in the naturalist's library for the books relating to the Hymenoptera of America alone—our wasps, bees, ants, and their smaller relatives, which engage everybody's attention by their social habits and amazing display of instincts. Besides these three principal and familiar groups the Hymenoptera include a host of other insects of great but inconspicuous importance. In large part these are parasitic on other insects or their larvæ, or even on their eggs, and some are the most minute insects known, virtually invisible to the unaided eye. Scarcely larger are the makers (Cynipidæ) of the galls so commonly seen on trees and plants in which they breed. Another group (Chalcidoidea) cause the swellings that disfigure plants by placing their young within their tissues, such as the "joint worms" that ruin grain; and here, again, many species are parasitic on grubs. Then there are the sawflies (Tenthredinidæ), resembling bees, whose ovipositors are like a pair of saws with which these insects are able to bore holes into wood, within which the egg is placed and the young larva burrows; of these are many and various kinds, all injurious to trees, garden shrubs and plants, each kind restricted to a particular sort of plant.
Perhaps even more numerous are the ichneumon flies, whose service in the world seems to be to keep the insect hosts down to the number possible to exist and at the same time to allow men and other animals to live. Their method of life is to deposit their eggs on or in the bodies of other insects, usually in the larval stage, where they hatch and thrive by the slow death of the host. The ichneumon flies are the dread of all other insects, most of whose adaptations for self-preservation are directed against this insidious and universal enemy to insect life.
None of the foregoing Hymenoptera live in colonies or by social methods. That plan belongs to the four most advanced divisions—wasps, bees, termites, and ants. Even among the wasps and bees, however, the larger number of species live alone or in single families, each female constructing a solitary receptacle for her purpose underground, in soft wood or otherwise. Most species store with the egg placed there half-dead insects, or pollen, etc., as food for the grub, which receives no further attention; but a few, such as the big digger wasp (Bembex) take food to the grubs daily. Another class of both wasps and bees form nests of several cells containing eggs, and thus in spring families are originated by fertilized females that have survived the winter. As the larvæ develop in succession they are fed by the mother, and presently mature sufficiently to aid her in caring for the younger grubs. Out of such family nests, or "combs" of paper cells, often attached to the ceilings of sheds and porches of rural houses, have apparently developed the mutually helpful societies of bees and ants, which are often of surprising extent and permanency.
The prosperity of these social insect communities, whose instincts, habits, and products amaze us, is due to an organized division of labor in the community between three classes of "citizens"—(1) the comparatively few males, whose whole duty is to fertilize the queen mother and supply the community with progeny; (2) the selected and specially nourished "queen"; (3) a vast number of nonreproductive females, the "workers," that build and guard the nest, gather and preserve stores of food (honey), and nurse and rear the young. In some groups the duties of the workers are subdivided among classes that differ in size and equipment. It is these female workers, or their correlatives among the solitary bees and wasps, that sting, their useless ovipositors having been transformed by the addition of poison into deadly weapons by which they procure their prey, or defend themselves, or both. It is this division of labor, and attendant habits, that especially characterize the higher Hymenoptera, and give to the order the supreme rank it occupies among insects.