Proceedings of the United States National Museum

A TREATISE ON THE ACARINA, OR MITES. By Nathan Banks, Custodian of Aradnvda. PREFACE. The mites have alwa\'.s attracted consideral)le interest, both from their minute size and because of the remarkable habits of man}^ species. Ahhough many have examined them in a desultor}^ way, Init few have really studied them. Consequently there is a great amount of literature by many persons, much of which is not reliable. Too often entomologists have considered that their knowledge of insects in general was a sufficient lâsis for the description of mites. Prob- ably the lack of general works on mites has been responsible for many errors. For years the only work treating of the mites as a whole that has been accessible to American naturalists is Andrew Murray's Economic Entomology; Aptera. In this ))ook, nearly 3()0 pages are devoted to Acarina. Unfortunately Murray's treatment is far from satisfactory and abundantly stored with mistakes, many, however, taken from other writers. Since that book was published several European specialists have been at work on the European fauna and produced monographs which are of great accuracv. Not only have many new facts been discovered, l)ut many of the old facts have ])een given quite new interpretations. Such a belief as the parasitism of the Uropoda on the Colorado potato- beetle seems hardly as yet to have been eradicated. To present a reliable text to the Aujerican reader is my intention. Very frequently I have obtained many facts of importance and interest from the European literature; particularly is this true with those parasitic groups with which 1 am not so well acquainted. Errors will, of course, be found, but great care has been exercised in choosing the sources of information. I have given tables to all the known American genera, and in some families added other well-known genera which will doubtless occur in our fauna when it is more thoroughlv explored. Practically the only door through which one may enter into the S3^stematic study of mites in general is Canestrini's Prospetto dell'Aca- rofauna Italiana. Proceedings U. S. National Museum, Vol. XXVIII—No. 1382. Proc. N. :\1. vol. xxviii—04 1 - 1 — PROCEEDINGS OF THE NA TIONAL MUSEUM. VOL. XXVIII. INTRODUCTION. The Acai'ians form lui order in the gw^nt ehiss Arachiiidu. Thev are thus related to spider.s, daddy-lono-deo-s, and scorpions. A few writers at various times have claimed that the mites were a separate class, l)ut tiie best sense of modern autliors is that they are g'enuine Arachnids, and in many ways closely related to Solpugids and Phalang-ids. Although quite easily recog-nized at sight, it is not so easy to give definite charactei's whereby to distinguish a mite from other Arach- nids. The abdomen and cepbalothorax are broadly united to each other, and often there is no distinction l)etween these parts. Usuallv there is no trace of segmentation, but in some forms it is (piite distinct. Eyes ar(^ often present, but rarely only a median pair as we find in Phalangids and Solpugids. The "^^ • mouth segments have Ijecome united to b form a lêak, rostrum, or capitulum. How- '^ ever this is not easily made out in some '^ forms. Commonly tiie larva at birth has but three pairs of legs, and ol)tains the •^ fourth pair only after a molt and meta- morphosis. In the ^ -:ig Eriophyidte, how- / cvei-, there are l)ut two pairs of legs in f / \ ,\ I botli adult and young, and in l*frr<)j>ti(s I /y\ the young have eight legs at l)irth. The adult mite has (except in the Eriophyid;e) four pairs of legs; often arranged in two groups, the hinder pairs apparentl v arising from the abdomen. However it is not prc^bable that such is the case; rather the coalescence of the abdomen and cephalo- 1. ^ Fiij Dorsal view of a mite, (i, . , mandibles; 6, palpi; r, leg I; d, thorax has effaced the true outlines of these ^î5^;":'iI^r?^t™^t^ ^ Portions.^ It is probable that the a},domen of mites is more than the abdomen of other Arachnids. If one examines a So/j)u(/a, he sees that the cephalothorax is divided into several portions, and it may be that the cephalothorax of mites represents only the anterior of these, while the al)domen of mites represents the abdomen of S()lj)\uja phis the two posterior divisions of the cephalothorax. In T((r-'«>)icnius^ and some other genera, the a))domen shows on the dorsum distinct traces of segmentation. On the venter there is still less distinction between parts, and in several groups, as Ixodidty and some Gamasidt\i, the genital segment is pushed forward between the legs so far that the genital aperture is close to the mouth. In other forms the genital opening is at the extreme tip of the body, and the anus is upon the dorsum. NO. 1382. THE ACARINA OR MITES—BANKS. 3 The cephalothorax. or anterior part of the boch', commonly ha.s one or more pairs of .simple ocelli-like eyes. They are usually sessile, but sometime.s elevated on pedicels. The mouth-segments form typically a truncate cone or beak. Some- times it is partially or completely retracted into the bod\'. The mouth parts are the mandibles and palpi. P^requently there are other parts, as a hypopharynx, a lip, or detinitel^^ separated maxillae, as will be mentioned under each family. Several investigators have claimed that there are three or four mouth appendages, and there are structures in some forms that indicate three. The mandibles generally are of two joints. The last is often opposable to a projection of the preceding, so as to become chelate. However, in many forms the mandibles are slender, needle-like, and suited for piercing. In each of the three large families (Oribatidaj, Gamasidfe, and Tvroglyphida?) wdiich typi- calh' have chelate mandibles there is one genus with styliform piercing mandibles. The palpi have never more than live joints; the last is frequently provided with peculiar sensor}^ hairs. In some cases the palpi have a geniculate attitude. The various forms of palpi may be grouped into four classes. (1) Where they are simple, filiform, and have a tactile function; (2) where they are moditied for predatory pur- poses, being provided with spines, hooks, or claws; {?>) where the last joint is oppo.sable to the preceding, so that the mite may bv its palpi cling to some object; (4) where they have become obsolete, and are more or less united to the rostrum. The basal joints of the palpi are at times differentiated to form luaxilhv. In several families there is a distinct lingula. tongue, or hypostome, which arises from the inner base of the beak, and may be divided or simple. It ma\^ have a groove above, called the vomer. The hypostome is usuallv not visible except hy dissection, Ijut in the ticks it is ver}^ large and roughened with sharp teeth. Sometimes the ])a.sal joints of the palpi unite to form a lip, or labium. Above the mandibles in man}- forms is a thin corneous plate, known I as the epistoma. Its sides may be partlv united to the beak or lip below and thus form a tube, called the oral tube, for it is through it that the mandibles are protruded. The pharynx, or sucking portion of the alimentary tract, is sometimes prolonged forward into a sort of cone between the mouth-parts. The opening of the body into which the mouth-parts are inserted is known as the ; camerostome. In one group {JJi'opodci) the anterior legs are also inserted into this camerostome. ^ The adult mite generallj' has four pairs of legs, and the larva three pairs. It has been shown that the eml)ryo of certain forms {Gauiasus 1 and Ixodes) has four pairs of legs Ijefore birth, but one pair is aborted I to be again developed at the nymphal stage. This is an indication that the six-legged larva is a secondar}^ development, and lessens the 'l PROCEEDINGS OF THE NA TIONAL MUSEUM. VOL. XXVIII. apparent difference between Acarina and other Arachnida. The legs are composed of from five to seven segments; in some forms the apical joints are subdivided, ])ut do not form genuine segments. Tlie lengtli and character of the joints vary in the different families, ])ut usually there are distinguishable the following parts: coxa, trochanter, feuuir, patella, tibia, and tarsus. In some cases the femora are divided into two parts. The legs are provided with hairs and spines, sometimes moditied for some particular function. In several groups there are organs on the anterior legs which appear to have an auditory function. The last joint or tarsus is commonly terminated by from one to three claws or ungues. In some groups there is a difference in this respect between the young and the adult. The claws are not often toothed. In many cases there is a median cup-shaped sucker, pulvillus, caroncle, or ambulacrum ])etween the claws or bearing them. The reproductive organs, as in other Arachnids, open on the ventral surface of the abdomen near the ])ase. The female aperture (vulva or epigynum) is of various shapes, and sometimes closed by flaps or folding-doors. The male aperture (epian- drum) is usually smaller than that of the female. The body is often provided with hairs, bristles, or scales, which are of char- acteristic nature and arrangement in each species.

Load more