. Animal biology. Zoology; Biology. CLASS INSECTA 291 Some Lepidoptera are useful because their visits to flowers result in cross-pollination. Chalcid flies and ichneumon flies, which belong to the Hymenoptera, are beneficial because they attack the developmental stages or the adults of many injurious insects. The egg is laid on or in the host the soft tissues of which the developing larva destroys. The larva of one ichneumon fly attacks the borers in shade trees, and the fly is often seen laying its eggs in the trunks and larger limbs of such trees (Fig. 190). It is 1)-^ inches long and has a
. Animal biology. Zoology; Biology. CLASS INSECTA 291 Some Lepidoptera are useful because their visits to flowers result in cross-pollination. Chalcid flies and ichneumon flies, which belong to the Hymenoptera, are beneficial because they attack the developmental stages or the adults of many injurious insects. The egg is laid on or in the host the soft tissues of which the developing larva destroys. The larva of one ichneumon fly attacks the borers in shade trees, and the fly is often seen laying its eggs in the trunks and larger limbs of such trees (Fig. 190). It is 1)-^ inches long and has an ovipositor 6 inches long, with which it drills a hole through the wood into the burrow of the boring larva where it deposits an egg. Many seeing this insect at work hold it responsible for the injury to the tree which is caused by the concealed borer. 320. Social Insects. — Social instincts are exhibited by a consider- able number of insects, especially by termites and some beetles. Some lepidopterous larvae make communal webs. In the Hymenoptera, however, and especially among the ants, bees, and wasps, the most striking instances of insect societies occur. Among social insects the honeybee (Fig. 191) stands out not only as a type but also as that invertebrate which has been most intimately associated with mankind and has reached the highest degree of domes- tication. For ages before man learned how to manufacture sugar he depended for his sweets very largely upon the bees, and honey was an important element in human diet. A swarm, or society, of honeybees includes three distinct types— workers, drones, and queen. In a swarm of 60,000 individuals there are perhaps 200 drones and but one queen, all the rest being workers. Of the three types the queen is the largest, is distinguished by the greater length of her abdomen, and lives for many years. She lays all of the eggs from which are produced the rest of the members of the swarm. The workers are infertile females which do
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