Spider, a division of the insect order aracli-nida, which also includes the mites and scorpions. The general character of the order, which seems intermediate between crustaceans and insects proper, though nearest to the latter in mode of development, are given in the article Arachnida. The external envelope is usually soft and tough, but not corneous, and is provided with papillae, spines, bristles, and hairs, giving a furry or velvety, but generally disgusting aspect; the inner membrane of the skin is thin and colorless, and under it is a layer of colored vesicles and granules, the seat of the brilliant hues observed in many species.
The body is divided into thorax and abdomen, the head is continuous with the chest, and there are no wings. From the inner surface of the cephalothorax are given off various processes serving for muscular insertions, forming at the bottom a solid horizontal plate, a kind of internal skeleton attached to the sternal plates by ligaments. The. muscles are dirty yellow, transversely striated, and in general disposition like those of crustaceans; the principal masses are found in the cephalothorax, acting on the mouth, tactile organs, and legs; in those with an unarticulated abdomen there are numerous interlacing fibres encompassing this part, and sending processes among the organs and to the ventral tendinous ligament. The locomotive organs on the cephalothorax are four pairs of legs, of which the first in some resembles a posterior pair of metamorphosed jaws; each foot usually ends in two claws, but some have only one, and others three or four; each leg has usually seven joints; in some the tarsi have a great number of joints, which can be readily dropped off for the purpose of escape, and are reproduced at the time of the moult.
The central part of the nervous system is situated around the oesophagus, sending nerves to the head and limbs; the splanchnic nerves for the viscera are well developed. The antennas are transformed into the prehensile and masticatory mandibles; a delicate sense of touch resides in the palpi, and in the end of the feet, which are employed in constructing the web; the senses of taste, smell, and hearing have not been satisfactorily localized in any special organs. The eyes are smooth and simple stemmata, variously placed on the cephalothorax according to the mode of life of the species, usually eight, sometimes six, of different sizes, grouped symmetrically on the anterior median line or scattered on its lateral border, and directed accordingly upward or laterally; the diurnal species have the pigment greenish, reddish, or dark, and the nocturnal splendidly lustrous, as in the cats. The cheliceres or fangs have the form of bi-articulated antennae, the basal joint being very thick, and the terminal one a very sharp hook folded under the former when not in use, but capable of erection for defence or seizing prey, and having at the apex the opening of the duct of a poison gland; the first pair of maxillae are changed into very long tactile or prehensile organs, the upwardly directed prominences of whose basal joints cover the entrance of the mouth, and serve as bruising organs; there is also a tumid hairy upper lip; the borders of the oral cavity may be approximated so as to form a suctorial canal, as well as the very short and horny oesophagus.
The stomach is in the cephalothorax, and is divided behind the sucking apparatus into lateral halves extending in an arched manner in front, where they become contiguous or united into a ring, from which are given off four or five pairs of casca directed toward the insertion of the legs and palpi; the intestine arises from this annular stomach, traverses the abdomen on the median line, and before ending at the anus forms a cloacal dilatation; salivary glands exist in a cavity above the palate, communicating with the mouth by a slit in the upper lip; the liver is very large, enveloping most of the viscera, of a dirty yellow, made up of nu-merous branches and closely aggregated caeca, opening into the middle portion of the intestine. The blood is colorless; there is a heart, dorsal vessel with many constrictions, arteries, and vessels returning the blood from the respiratory organs. Respiration takes place both by pulmonary sacs and tracheae, one or the other penetrating all parts of the body and limbs; there are two sacs occupying the base of the abdomen, containing more or less lamellae; the blood penetrates to the respiratory system probably by a kind of infiltration.
Distinct urinary organs are present, much ramified glandular tubes pouring a whitish or reddish secretion into the cloaca. There are two poison glands at the base of the cheli-ceres, communicating with their terminal hook. The apparatus which secretes the viscid transparent liquid, hardening into silk on exposure to the air, consists of glandular follicles and tubes, of various forms and arrangement, in the midst of the abdominal organs; in most spiders there are three pairs (in some two) of jointed spinnerets or obtusely conical papillae behind the anus; the apex of these papillae is surrounded by stiff bristles and hairs, and is dotted with numerous horny tubes, the prolongation of the excretory ducts; the number of the tubes varies from 1,000 in epeira to less than 100 in the smaller species. The sexes are separate, and the eggs are numerous and spheroidal; a single impregnation is sufficient for several successive generations. There is generally only one brood in a year; the embryos are developed after the deposition of the eggs, and are hatched sometimes in a few weeks, and at others not till the following spring; the eggs are enveloped in a silken bag, from which the young are sometimes helped out by the mother; they resemble the parents except in size, and undergo no metamorphosis but change of skin; life may bo prolonged for several years.
Only the system of classification of Walckenaer will be briefly given here, as it places stress on the most interesting points in their economy, though not affording a sufficient basis for natural classification. He divides the spinning spiders into terrestrial and aquatic, as follows:
Venantes, always running or leaping near their abode in search of prey, with the families : 1, latebrico-Ice, hiding in holes and fissures, like mygale; 2, tubicoloe, enclosing themselves in silken tubes (dysdera, segestria); 3, cellulicoloe, living in small cells (scytodes); 4, cursores, swift runners (lycosa, ctenus); 5, saltatores, leaping with agility (attus).
Vagantes, wandering after prey, without fixed residence except while laying eggs, with family 6, laterigradoe, walking and running sideways or backward, and occasionally throwing out threads to entrap their prey (thomisus).
Errantes, prowling in the neighborhood of their nests or threads, with families: 7, niditeloe, going abroad, but making a web whence issue threads to entrap prey (clubiona, drassus); 8, filiteloe, spreading long threads about their prowling places (phol-cus, clotho).
Sedentes, spinning large webs and lying in wait in the middle or at the side, with families : '9, tapiteoe, spinning large webs of close texture in which they dwell (tegenaria, agelena); 10, orhiteloe, spreading orbicular or spiral webs of a regular open texture, living in the middle or at the side (epe'ira); 11, retiteloe, spinning irregular webs of open meshes, re- . maining in the middle or on the side (theridion).
Swimmers Natantes, spreading filaments in water, with family: 12, aquiteloe (argyroneta). - Spiders are found in every habitable portion of the globe, but are largest in warm climates; the males and females live separately, and the latter are most frequently seen and are considerably the larger; all are carnivorous, devouring living prey, sucking the juices and sometimes swallowing the fragments; the females are generally ready to attack and feed on the males, even in the reproducing season, and both sexes are fond of fighting, the vanquished being devoured; they can support long fasts, and remain torpid during the winter; they are very cleanly, and spend much time in clearing their limbs from dust and dirt by the toothed combs and brushes on the mandibles. In making their webs they accommodate themselves remarkably to circumstances, displaying great perseverance, ingenuity, and almost intelligence; they carefully guard their eggs, sometimes carrying about with them the silken bag which contains them, and are affectionate to their young, which in some cases devour their mother. They descend by their silken threads head downward, but climb up on them head upward, rolling them into a bundle during the ascent; the thread cannot be used a second time for the same purpose.
When they wish to go from tree to tree, some let go a thread in the direction of the wind, and when it has reached the object they strengthen and pass over it, in this way travelling long distances without descending to the ground; their tiny cables are very abundantly seen in dewy mornings of spring and autumn; some small gossamer spiders even speed through the air buoyed up by their light threads. They are capable of some domestication; Pelisson, a prisoner in the Bas-tile, had a pet spider which came regularly, at the sound of a musical instrument, to get its meal of flies; and a spider raiser in France is said to have tamed 800, which he kept in a single apartment for their silk. The supply of the silk of the spider seems to be limited to sufficient to make six or seven webs in a season; it is very strong and very fine, and is used in astronomy for the divisions of the micrometer; according to Leeuwenhoek, it takes 4,000,000 of the extremely delicate threads from the thousands of spinnerules to make a filament as large as a human hair; each thread of the spider as used in the web is made up of thousands of smaller ones; one or all the spinnerets may be used as occasion requires.
Attempts have been made to render the silk of the spider available for manufacturing purposes, but with little success. (See Cobweb, and Silk Spider.) Spiders are eaten by many barbarous tribes of men, as the American Indians, S. Africans, and Australians; they also supply abundant food to many birds, reptiles, and carnivorous insects. They are affected and frequently destroyed by parasitic mites, and their eggs serve •to nourish the young larvae of several species of ichneumon flies; the smallest puncture in the chest or abdomen is fatal from the impossibility of arresting the escape of the nutrient fluids; their colors fade rapidly after death, even in preservative liquids. A single wound from a spider will soon kill the domestic fly; the large crab spiders of South America (my-gale) leap upon and destroy humming birds and creepers, and produce dangerous and occasionally fatal symptoms in debilitated persons; every physician knows that even the bite of the smaller spiders of temperate climates may pierce the skin in certain localities, and cause painful irritation. - For descriptions and figures of the species of the United States see papers by N. M. Hentz in Vols. iv., v., and vi. of the "Boston Journal of Natural History" (1841-'57), now in course of republication, with figures by the same society (1875). The genus mygale (Walck.) contains the largest of the spiders, of dark colors, nocturnal, living in galleries which they make in the ground, in clefts of trees, crevices in rocks, or among leaves.
The crab or bird spider of South America (M. aricularia, Walck.) is about 3 in. long, its legs extending over a space of 8 or 10 in.; the body is very hairy and blackish, and the ends of the feet are reddish; it is very powerful, jumping upon and killing small birds; it spins no web; its cell is in the form of a pointed tube, of a white firm tissue. There are some large species in the southern states, feeding principally on the large orthoptera, believed by the Indians to possess valuable medicinal properties, and eaten accordingly. A large species (M. Hentzii) in Texas is called there tarantula; other species in California are called trap-door spiders, from their hollowing a more or less conical nest, about 3 in. long and an inch in diameter, in the clayey soil; the nests are lined with silk, with an accurately fitting lid, so arranged that the inmate can firmly hold it down against ordinary enemies; the cover outside so nearly resembles the surrounding earth in color and roughness as to be recognized with difficulty.
For an account of the curious devices in the interior arrangement of these nests, see "Proceedings of the Boston Society of Natural History" for 1875. The species of the genus lycosa (Latr.) are well called wolf spiders, for they are the most savage, voracious, and quarrelsome of the family; they make no web, but prowl on the ground by night, running very fast, and hiding in natural or artificial boles in the ground, which they strengthen with silk; the females carry the cocoon attached to the posterior part of the body, and defend it with the greatest courage, some guarding it under stones; the young when hatched climb on the abdomen of the mother, giving her a monstrous appearance, and are said finally to devour her. One of the largest and most common species is the L. fatifera (Hentz), about 1½ in. long, hairy, and bluish black; it is as large as the tarantula of Europe, which belongs to this genus, and is not uncommon in Massachusetts; it must rarely bite persons, from its habits and haunts, though its poison may produce ill consequences if introduced under the skin, not however to be compared with those from the mygale of the tropics; it is very savage and tenacious of life.
The genus attus (Walck.) includes the small species commonly called jumping spiders; they make no web, wander in search of prey, and cast the skin and hibernate in silken-valved recesses; they are common in summer on walls and windows in the sun, walking by jerks, crawling stealthily up to flies, and jumping with rarely failing accuracy when near enough. The best known jumping spider in New England is the A. familiaris (Hentz), about ½ in. long, pale gray and hairy, the abdomen blackish with a grayish angular band; it is very common in houses, dwelling in cracks on the outside, and wandering about in the sun in search of food; before leaping at a fly, it fixes a thread to secure itself from falling. It is widely distributed. Its backward gait is as rapid as its forward. The long-legged spider (pholcus Atlanticus, Hentz) is about ½- in. long, with a narrow body and very long slender legs, which are easily separated at the will of the animal when seized by them; the color is pale gray; it is common in corners of dark and rarely used rooms, in cellars and churches, spinning a very loose web crossed in all directions, which is very rapidly shaken when touched; the eggs are carried in the jaws, enveloped in a silken bag, and about 200 young are rolled in a ball not larger than a pea; the food consists of very small insects, though they eagerly devour each other, especially when young; they are favorite food for wasps, who store their cells with them as a provision for their young.
The European representative is the P. phalangioides (Walck.). The common house spider (tegenaria medicinalis, Hcntz) is found in every house and cellar in the land; the cheliceres are moderate, and the fourth pair of feet the longest; the upper two spinnerets are remarkably larger than the others, and the four anterior eyes in a line curved backward. It is sedentary, making in an obscure corner a large and nearly horizontal web, with a tubular habitation at the upper part; it is not quite an inch long, varying in color from pale brown to bluish black according to the absence of light in its retreat, with a dark band on each side of the thorax, and the abdomen and feet varied with blackish; the specific name is derived from the use formerly made of the web in cases of fever. In epe'ira (Walck.) the web is either vertical or inclined, and the threads are arranged in a more or less regularly geometrical manner, radiating from the centre, where the animal remains, according to the absence of disturbing causes. The common epe'ira (E. vulgaris, Hentz) is less than an inch long, with a full body, gray with blackish abdomen, with winding white marks and a white cross in the middle; it may almost be said to be domesticated, its geometrical web being so often met with near the windows of houses.
The webs of the spider, like the cells of the bee, are not geometrically perfect; their irregularity can generally be detected even by the unassisted eye. - The long-logged, round-bodied spider, commonly called "father long-legs," is one of the trachearian arachnids, so named from the respiratory organs being radiated tracheae, receiving air through two Stigmatic openings; it is the harvest spider (phalangium cornutum, Linn.) in Europe, and an allied species in the United States. The eyes are two; the mandibles end in double pincers; the legs are eight, slender, and when separated from the body exhibit signs of irritability for some time. They are harmless, preying upon mites and small insects, and are very common in the fields. - Many small spiders rly about on their silken threads, carried far by currents of wind. - Of the arachnida, the scorpions appeared first in the carboniferous epoch, and the true spiders in the Jurassic age. - See "American Naturalist," vols. v. (May, 1871), vi. (March, 1872), and viii. (October, 1874), for descriptions and figures.
See also various articles on spiders by Dr. Burt G. Wilder, in "Proceedings of the American Association for the Advancement of Science," 1873, and the "Popular Science Monthly," April, 1875. For further details see chap, xviii. of Rennie's "Insect Architecture," the works of Kirby and Spence, and particularly the Histoire des insectes apteres (Nouvelles suites a Bu.ffon), by Baron Walcke-naer (vols, i., ii., and iii., 8vo, Paris, 1837-'44). (See Mite, Scorpion, and Silk Spider).
Wolf Spider (Lycosa fatifera).
Jumping Spider (Altus familiaris).
Common House Spider (Tegenaria medicinalis).
Common Epe'ira (Epeira vulgaris).