The genus TROMBIDIUM has recently been subdivided by Berlese into a number of smaller ones, of which some five or six occur in the United States. The mature mite is not parasitic but the larvæ which are very numerous in certain localities will cause intense itching, soreness, and even more serious complications. They burrow beneath the skin and produce inflamed spots. They have received the popular name of "RED BUG." The names LEPTUS AMERICANUS and L. IRRITANS have been applied to them, although they are now known to be immature stages. (Fig. 44.) HEXAPODA (Insecta) The Thysanura (springtails and bristletails), the Neuropteroids (may-flies, stone-flies, dragon-flies, caddis-flies, etc.), Mallophaga (bird lice), Physopoda (thrips), Orthoptera (grasshoppers, crickets, roaches), are of no special interest from our viewpoint. The remaining orders are briefly characterized below. SIPHUNCULATA (page 275) Mouth parts suctorial; beak fleshy, not jointed; insect wingless; parasitic upon mammals. Metamorphosis incomplete. Lice. HEMIPTERA (page 275) Mouth parts suctorial; beak or the sheath of the beak jointed; in the mature state usually with four wings. In external appearance the immature insect resembles the adult except that the immature form (i.e. nymph) never has wings, the successive instars during the process of growth, therefore, are quite similar; and the metamorphosis is thus incomplete. To this order belong the true bugs, the plant lice, leaf hoppers, frog hoppers, cicadas, etc. LEPIDOPTERA The adult insect has the body covered with scales and (with the rare exception of the females of a few species) with four wings also covered with scales. Proboscis, when present, coiled, not segmented, adapted for sucking. Metamorphosis complete, i.e. the young which hatches from the egg is quite unlike the adult, and after undergoing several molts transforms into a quiescent pupa which is frequently enclosed in a cocoon from which the adult later emerges. The larvæ are known as caterpillars. Butterflies and moths. DIPTERA (page 285) The adult insect is provided with two, usually transparent, wings, the second pair of wings of other insects being replaced by a pair of halteres or balancers. In a few rare species the wings, or halteres, or both, are wanting. The mouth parts, which are not segmented, are adapted for sucking. The tarsi are five-segmented. Metamorphosis complete. The larvæ, which are never provided with jointed legs, are variously known as maggots, or grubs, or wrigglers. Flies, midges, mosquitoes. SIPHONAPTERA (page 316)