larva may show that a more perfect nutrition is obtained from a well-constructed cylinder, and if so this would to a slight extent satisfy our longing for explanation, though throwing no light whatever on the physiology or psychology of the artificer, and leaving us hopelessly perplexed as to why a beetle in ages long gone by should or could adopt a mode of life that by long processes of evolution should, after enormous difficulties have been overcome, attain the perfection we admire.[153] FAM. 82. SCOLYTIDAE.—_Rostrum extremely short, broad; tibiae frequently denticulate externally; antennae short, with a broad club._ This family is not at all sharply distinguished from certain groups of Curculionidae (from Cossonides _e.g._), but as the species have somewhat different habits, and in the majority of cases can be readily distinguished, it is an advantage to separate the two families. About 1400 species are at present known. Most of them are wood- and bark-feeders; some bore into hard wood; a few mine in twigs or small branches of trees, but the majority live in the inner layers of the bark; and this also serves as the nidus of the larvae. A small number of species have been found to inhabit the stems of herbaceous plants, or to live in dry fruits. Owing to their retiring habits they are rarely seen except by those who seek them in their abodes, when they may often be found in great profusion. The mother-beetle bores into the suitable layer of the bark, forming a sort of tunnel and depositing eggs therein. The young larvae start each one a tunnel of its own, diverging from the parent tunnel; hence each batch of larvae produces a system of tunnels, starting from the parents' burrow, and in many species these burrows are {295}characteristic in form and direction, so that the work of particular Scolytids can be recognised by the initiated. The Platypides bore into the wood of trees and stumps; they are chiefly exotic, and little is known about them. They are the most aberrant of all Rhynchophora, the head being remarkably short, flat in front, with the mouth placed on the under surface of the head, there being no trace of a rostrum: the tarsi are elongate and slender, the third joint not being at all lobed, while the true fourth joint is visible. Hence they have not the appearance of Rhynchophora. Some authorities treat the Platypides as a distinct family. Some of the members of the group Tomicides also bore into the wood. Recent observations have shown that there is an important feature in the economy of certain of these wood-borers, inasmuch as they live gregariously in the burrow, and feed on peculiar fungi that develop there, and are called ambrosia. According to Hubbard[154], some species cultivate these fungi, making elaborate preparations to start their growth. The fungi, however, sometimes increase to such an extent as to seal up the burrows, and kill the Insects by suffocation.