The question of the destruction of the mites in the field is sometimes an important one, and under some conditions, is feasible. Chittenden states that much can be accomplished by keeping the grass, weeds, and useless herbage mowed closely, so as to expose the mites to the sun. He believes that in some cases good may be done by dusting the grass and other plants, after cutting, with flowers of sulphur or by spraying with dilute kerosene emulsion in which sulphur has been mixed. More recently (1914) he calls attention to the value of cattle, and more especially sheep, in destroying the pests by tramping on them and by keeping the grass and herbage closely cropped. IXODOIDEA OR TICKS Until recently, the ticks attracted comparatively little attention from entomologists. Since their importance as carriers of disease has been established, interest in the group has been enormously stimulated and now they rank second only to the mosquitoes in the amount of detailed study that has been devoted to them. [Illustration: 45_a_. Argus persicus. Capitulum of male. After Nuttall and Warburton.] The ticks are the largest of the Acarina. They are characterized by the fact that the hypostome, or "tongue" (fig. 45) is large and file-like, roughened by sharp teeth. They possess a breathing pore on each side of the body, above the third or fourth coxæ (fig. 45_b_). [Illustration: 45_b_. Left spiracle of nymph of _Argas persicus_. After Nuttall and Warburton.] There are two distinct families of the IXODOIDEA, differing greatly in structure, life-history and habits. These are the ARGASIDÆ and the IXODIDÆ. We shall follow Nuttall (1908) in characterizing these two families and in pointing out their biological differences, and shall discuss briefly the more important species which attack man. The consideration of the ticks as carriers of disease will be reserved for a later chapter. Argasidæ In the ticks belonging to the family ARGASIDÆ, there is comparatively little sexual dimorphism, while this is very marked in the Ixodidæ. The capitulum, or so-called "head" is ventral, instead of terminal; the palpi are leg-like, with the segments subequal; the scutum, or dorsal shield, is absent; eyes, when present, are lateral, on supracoxal folds. The spiracles are very small; coxæ unarmed; tarsi without ventral spurs, and the pulvilli are absent or rudimentary. In habits and life history the Argasidæ present striking characteristics. In the first place, they are long-lived, a factor which counts for much in the maintenance of the species. They are intermittent feeders, being comparable with the bed-bug in this respect. There are two or more nymphal stages, and they may molt after attaining maturity. The female lays comparatively few eggs in several small batches.