CHAPTER IV.

GROWTH OF SPIDERS.

Persons unfamiliar with spiders find it hard to tell young from old, and male from female. This is caused, in part, by the great differences between different ages and sexes of the same spider, on account of which they are supposed to belong to distinct species.

The adult males and females are easily distinguished from each other, and from the young, by the complete development of organs peculiar to each sex, which will be described further on.

The males are usually smaller than the females, and have, in proportion to their size, smaller abdomens and longer legs. They are usually darker colored, especially on the head and front part of the body; and markings which are distinct in the female run together and become darker in the male. In most species these differences are not great; but in some no one would ever suppose, without other evidence, that the males and females had any relationship to each other. The most extreme cases of this kind are _Argiope_ and _Nephila_, where the male is about a tenth as large as the female. Fig. 43 represents male and female of _Nephila plumipes_ described by Wilder.

The female of one of the common crab spiders is white as milk, with a crimson stripe on each side of the abdomen; while the male is a little brown-and-yellow spider, with dark markings of a pattern common in the family to which it belongs.

In the genus _Erigone_, which includes the smallest known spiders, the males often have curious humps and horns on their heads, Fig. 44. The most extreme example is Fig. 45, where the eyes are carried up on the end of the horn. The females of all these species have plain round heads; and what use the humps are to the males nobody knows.

The peculiar organs by which the adult males and females can always be distinguished are, in the males, the palpal organs, on the ends of the palpi; and, in the females, the epigynum, Fig. 1.

PALPAL ORGANS.

As the male spider gets nearly full grown, the terminal joints of the palpi become swollen, and, after the last moult, the palpal organs are uncovered.

The simplest form of palpal organ is found in the large _Mygalidæ_, Fig. 6. It consists of a hard bulb, Fig. 46, drawn out to a point, in which is a small hole leading to a sac within.

In most spiders the terminal joint is flattened, and has a hollow on the under side, in which the palpal organ is partly concealed. The bulb is flattened to fit this hollow; and the point of it is prolonged into a distinct tube of various shapes, furnished with numerous spines and appendages. Fig. 47 is the palpal organ of _Epeira vulgaris_ flattened out, and made transparent. The internal sac is shown at _a_; and the tube from it _b_ runs round the inside of the bulb, and ends at the opening _c_. The outside of the organ has various horns and appendages. Fig. 48 is the palpus of another spider, where the outer tube is so long, that it is coiled up over the basal part of the bulb; and the end rests on a strong spine at one side of the palpus.

Not only the terminal joints of the palpi, but also the next, and sometimes next two joints, are modified in shape, with the development of the palpal organ, Fig. 48. The shape of these organs is very constant in the same species of spider, and thus becomes one of the most convenient marks of such a group.

THE EPIGYNUM.

When the female spider is nearly full grown, there appears a hard, swollen place just in front of the opening of the ovaries, Fig. 1; and, after the last moult, the epigynum is uncovered at this place. The epigynum, Fig. 49, consists of two spermathecæ, E, which connect by two little tubes, H, H, with the oviduct near its mouth, and by two larger tubes, D, with the outside of the spider. The mouths of these larger tubes are often surrounded by various hard appendages to support and guide the palpal organs when the latter are thrust into them. These parts, like the palpal organs, furnish convenient marks for distinguishing species. The spermathecæ, E, vary but little in shape in different spiders; but the tubes H and D are often lengthened, and twisted into shapes nearly as complicated as those of the palpal organs. Fig. 50 is the epigynum of a small _Theridion_, where the arrangement of parts can be very distinctly seen. E, E, are the spermathecæ; H, H, the tubes opening into the oviduct; and D, D, the tubes opening outward. Fig. 51 is the epigynum of another closely allied species, where the tubes D, D, are very much elongated and twisted up, corresponding to the long discharge-tube of the palpal organ of the male of the same spider, Fig. 48.

USE OF THE PALPAL ORGANS AND EPIGYNUM.

When the reproductive cells of the male spider are mature, he discharges the liquid containing them on a little web spun for the purpose; dips his palpal organs into it, and in a few moments takes up the whole, it is supposed, into the little sacs, Figs. 47, 48, inside the bulb; then he seeks the female, and inserts the palpal organs into her epigynum. The soft part at the base of the organ swells up, and presses in the discharge-tube, and probably forces out the contents of the bulb into the spermathecæ, E, E, from which it escapes, in course of time, by the tubes, H, H, into the oviduct, and fertilizes the eggs about the time they are laid.

One palpal organ is usually inserted at a time, and, after a while, taken out, and replaced by the other; this change being repeated many times by the same spider. Among the _Lycosidæ_, Fig. 10, the male leaps on the back of the female, and is carried about by her, Fig. 52. He reaches down at the side of her abdomen, and inserts his palpi in the epigynum underneath. In _Linyphia_ and _Theridion_ the male and female live peaceably together for a long time in the same web. The male reaches from in front under the female, Fig. 53, and inserts his palpal organs, one after the other, for hours together. In _Agalena_ the male is the stronger of the two sexes. He takes the female in his mandibles, and lays her on one side, Fig. 54, and inserts one of his palpi. After a time, he rises on tiptoe, turns her around and over, so that she lies on the other side, with her head in the opposite direction, and inserts the other palpus. The female lies as though dead. In _Nephila_ and _Argiope_, where the male is very small, he stands on the upper edge of the web while the female is in her usual position in the centre. After feeling the web with his feet for some time, he runs down to the centre so lightly as not to disturb the female, and climbs about over her body for some minutes, in an apparently aimless way. She takes no notice of him at first; but at length, especially if he approach the under side of her abdomen, she turns, and snaps at him with her jaws. He is usually nimble enough to dodge between her legs, and drop out of the web, and, after a while, climbs up to the top, and begins over again. In these encounters the males are often injured; they frequently lose some of their legs: and I have seen one, that had only four out of his eight left, still standing up to his work.

At length the male succeeds in getting under the female’s abdomen, and inserting his palpi into the epigynum. Fig. 55 shows the female hanging in the web, with the male at _a_, with his legs grasped around her abdomen.

The habits of these spiders furnish the grounds for the popular story, that female spiders regularly eat the males. No doubt it occasionally happens, where the female is the larger of the two; but in many species they live together for some time in the same web, or in a nest spun for the purpose; in some cases, before the female has reached the adult state.

LAYING EGGS.

When the eggs are mature, the female proceeds, like the male, to make a little web, and lays the eggs on it. Then she covers them over with silk, forming a cocoon, in which the young remain till some time after they are hatched. The laying of the eggs is seldom seen; for the spider does it in the night, or in retired places; and often, in confinement, refuses to lay at all.

The female _Drassus_, Fig. 56, spins a little web A across her nest, and drops the eggs E on it, as in the figure. They are soft, and mixed with liquid, and are discharged in one or two drops, like jelly. They quickly soak up the liquid, and become dry on the surface, sometimes adhering slightly together.

After the eggs are laid, the spider covers them with silk, drawing the threads over them from one side to the other, and fastening them to the edges of the web below. When the covering is complete, she bites off the threads that hold the cocoon to the nest, and finishes off the edges with her jaws.

The _Lycosidæ_ make their cocoons in the same way, but rounder, and showing only slightly the seam where the upper part was attached to the lower.

The _Lycosas_ carry their cocoons about, attached to the spinnerets, as in Fig. 57, bumping them over the stones without injury to the young inside.

Many spiders make their cocoons against a flat surface, where they remain attached by one side. _Attus mystaceus_ spins, before laying, a thick nest of white silk on the under side of a stone. In this she thickens a circular patch on the upper side, next the stone, and discharges her eggs upward against it, Fig. 58. They adhere, and are covered with white silk. I once had a spider of this species lay her eggs, in confinement, in a nest the under side of which had been cut away. Instead of completing the cocoon properly, she ate the eggs immediately after laying. _Epeira strix_ spins, before laying, a bunch of loose silk, Fig. 59. She touches her spinnerets, as in the figure on the left, draws them away a short distance, at the same time pressing upward with the hind-feet, as in the figure on the right; then moves the abdomen a little sidewise, and attaches the band of threads so as to form a loop. She keeps making these loops, turning round, at the same time, so as to form a rounded bunch of them, into the middle of which she afterwards lays the eggs, as in Fig. 60. The eggs, which are like a drop of jelly, are held up by the loose threads till the spider has time to spin under them a covering of stronger silk. _Epeira vulgaris_ makes a similar cocoon upward, downward, or sidewise, as may be most convenient.

Most of the _Theridiidæ_ make cocoons of loose silk, held up in the web by numerous threads. Some hang the cocoon by a stem, Fig. 61.

The large species of _Argiope_ makes a big pear-shaped cocoon hanging in grass or bushes, Fig. 62. A stem of loose brown silk is first made, and under this the eggs attached (at any rate this had been done in one which had been abandoned unfinished); then a cup-shaped piece is made under the eggs; the bunch of loose silk is spun over all, and finally the paper-like shell.

ESCAPE FROM THE COCOON.

These cocoons of _Argiope_ are made late in the summer, and the young stay in them till the next season. Out of six hundred cocoons collected by Wilder in the spring, less than a quarter were entire, the rest being pierced, or torn in some way, by birds or insects; so that the spiders were saved the trouble of gnawing their way out, as they can if obliged to.

I once noticed a small _Theridion_ gnawing at its soft cocoon, and found that one side had been made in this way much thinner than the rest of the cocoon. I put her, with the cocoon, in a bottle where I could watch her; and she soon commenced biting again, and kept it up the rest of the day. The following night the young came out.

Many spiders remain by their cocoons till the young come out; but other species, making similar ones, go away, or die, and the young get out themselves when they are old enough.

The young of _Micaria_ cut a smooth round hole in their paper-like cocoon, just large enough for them to come out one by one.

PARASITES.

The eggs in the cocoon are very liable to be eaten by parasitic insects. Certain wingless _Hymenoptera_ are always hunting around in the neighborhood of spiders’ nests, and may sometimes be seen trying to stick their ovipositor through a cocoon. If they succeed, their eggs hatch before the spiders, and eat the latter up. Other parasites lay eggs on the backs of young spiders, and the larva lives attached to the outside till it gets nearly as large as the spider itself.

GROWTH IN THE EGG.

The egg of a spider, like that of any other animal, is a cell which separates from the body of the female, and afterwards unites with one or more cells which have separated from the body of the male. This fertilization of the eggs probably takes place when they have reached their full size, and are about to be laid.

After the eggs are laid and hardened, it is very easy to watch their development. They grow just as well anywhere else as in the cocoon, and, in order to see through the shell, it is only necessary to cover the egg to be examined, with oil, alcohol, or any liquid that will wet it.

Just after it is laid, the egg looks like Fig. 63, _a_; or, if the egg is more opaque, only the ends of the lobes can be seen like irregular lumps. The first sign of growth is the division into two, Fig. 63, _b_. These divide into four, into eight, and so on, Fig. 63, _c_, _d_. At first the divisions are all alike; but at length they divide into two kinds,—small ones, with a dark spot in the middle, which cover the outside of the egg; and larger ones that occupy the inside. Fig. 63, _e_, shows an egg at this stage, where the large inner cells show through the layer of outer ones. Fig. 63, _f_, is a section of the same egg. The stages shown in _b_ and _c_ are seldom clearly seen, because the divisions are crowded together and too opaque; but _d_ and _e_ can be watched in any common spider’s eggs. The rate of growth varies according to circumstances. Some eggs laid in autumn develop slowly all winter, while others laid in summer are ready to hatch in a fortnight.

In the eggs of the long-legged cellar spider, laid in June, in about four or five days the young spider becomes lengthened out into a sort of barrel shape; and six whitish rings run half way round it, on each of which appears soon after a pair of little knobs, one each side, Fig. 64, _a_. These are the six segments of the thorax, and the six pairs of limbs; and their gradual growth is shown in Fig. 64, _b_, _c_, _d_. In _a_ there is no sign of a head or abdomen, except the more opaque ends of the embryo; but shortly after there appears an opaque knob at one end, Fig. 64, _b_, under which is a pair of little knobs, such as appeared at first on the thoracic segments; then appear two pairs, then three, and so on, till there are six pairs, which mark the six segments of the abdomen. Up to this time, the embryo has been rolled up with the under side outward; but now it begins to turn, and in a day or two has its back outward, Fig. 64, _c_. The constriction between the thorax and abdomen begins about this time; and in a few days more the spider is ready to hatch, Fig. 64, _d_.

YOUNG SPIDERS.

The hatching occupies a day or two. The shell, or rather skin, cracks along the lines between the legs, and comes off in rags; and the spider slowly stretches itself, and creeps about. It is now pale and soft, and without any hairs or spines, and only small claws on its feet; but, in a few days, it gets rid of another skin, and now begins to look like a spider. The eyes become darker colored; marks on the thorax become more distinct, and a dark stripe appears across the edge of each segment of the abdomen. The hairs are long, and few in number, and arranged in rows across the abdomen and along the middle of the thorax, Fig. 65. Before the next moult, they usually leave the cocoon, and for a time live together in a web spun in common. A brood of young _Epeira_ may often be seen looking like a ball of wool in the top of a bush, while below them, connected by threads to their roost, are the skins left at their second moult, and farther down, also connected by threads, the cocoon with the first skins.

_Dolomedes_ spins a nest in which the young live for a while after hatching.

The young of the running spiders, _Lycosidæ_, when they come out of the cocoon get on their mother’s back, and are carried round by her for some time.

Where large broods of young spiders live together, they soon begin to eat one another; and, if kept in confinement, one or two out of a cocoon full, may be raised without any other food.

Wilder noticed this in _Nephila plumipes_, and believes it is the natural habit of young spiders, and not the result of confinement.

As spiders grow larger, they have to moult from time to time. This process is shown by Wilder in Figs. 66, 67; and I have seen the same operation in _Argiope_. The spider hangs herself by a thread from the spinnerets to the centre of the web. The skin cracks around the thorax, just over the first joints of the legs; and the top part falls forward, being held only at the front edge. The skin of the abdomen breaks irregularly along the sides and back, and shrinks together in a bunch. The spider now hangs by a short thread from the spinnerets, and works to free her legs from the old skin, Fig. 66. This takes about quarter of an hour; and then she drops down, hanging by her spinnerets like a wet rag, Fig. 67.

If struck while in this condition, she can do nothing, not even draw her legs away. After ten or fifteen minutes, the legs begin to strengthen; and she draws them gradually up toward her, works them up and down a few times, and is soon able to get into the web again.

Blackwall observed nine moults in _Tegenaria civilis_, a spider that lives several years. Many species, and among them some of the largest, live only one year, hatching in the winter, leaving the cocoon in early summer, and laying eggs and dying in autumn. Other species seem to require two years for their growth; hatching in summer, passing their first winter half grown, growing up the next summer, but laying no eggs till the second spring. Some species are found adult at all seasons, and may live several years.

After spiders have passed their second moult, they usually live in the same places, and follow the same habits, as the adults.

The running spiders live usually on the ground, often near water, but some kinds in the hottest and dryest places. A few species live near water, and are accustomed to run about on its surface, without becoming wet. The _Theridiidæ_ almost all live in the shade, and always upside down in their webs. Some species live always in caves; and one in the deepest part of the Mammoth Cave has no eyes. Some spiders live only on high mountains, never appearing below the tree line. Some species seem to prefer certain kinds of plants. The horizontal branches of spruces, for instance, are particularly convenient for the webs of some species of _Theridion_. The water-spider, that builds its nest and lives on water-plants, has been already mentioned, and also the _Argyrodes_, that makes its home in the webs of other spiders. During winter immense numbers of spiders that have spent the summer under stones, in webs, and on plants, hide away among fallen leaves, and there live through the coldest and wettest weather, ready to move on the first warm day. During a thaw they often come out on the snow in great numbers.

Several house spiders have probably been imported, like rats, and are found all over the world; while other most common species never spread beyond the countries where they are most abundant.

BOOKS ABOUT SPIDERS.

CLASSIFICATION.—Thorell’s “Genera of European Spiders,” in “Acta Regiæ Societatis Scientiarum Upsalensis,” 1869, and Thorell’s “Synonymes of European Spiders,” contain a complete history of the classification of the spiders of Northern Europe, with references to all the descriptions of genera and species, and remarks on the use of names and groups by different authors. The great resemblance between the European and North-American spider faunæ make these the most useful books for American students. Simon’s “Arachnides de France,” a work not yet completed, describes all the spiders in France, and refers to descriptions of the other European species. It contains tables by which the genus and species to which any spider belongs can be found by the use of a few prominent characters.

ANATOMY.—Siebold’s “Anatomy of the Invertebrata” contains a good general account. Bertkau describes, in “Traschel’s Archiv für Naturgeschichte,” the mandibles in 1870, the respiratory-organs in 1872, and the sexual organs in 1875. Oeffinger describes the spinning-glands in “Archiv für Microscopische Anatomie,” 1860.

EMBRYOLOGY.—Claparède, Utrecht, 1862, and Balbiani, in “Annales des Sciences Naturelles,” 1872, describe the growth of the egg from segmentation to hatching. H. Ludwig, in “Zeitschrift für Wissenschaftliche Zoölogie,” 1876, gives an account of the segmentation in eggs of Philodromus.

HABITS.—Walckenaer’s “Histoire Naturelle des Apteres” goes over the whole subject. Blackwall, in “Researches in Zoölogy,” 1834, describes the web-making of Epeira, and the flying habits of spiders. Blackwall also writes on habits in “The Spiders of Great Britain and Ireland,” published by the Ray Society, 1864, and in various papers in “Transactions of the Linnæan Society,” 1833 to 1841. Menge’s Lebensweise der Arachniden in “Schriften der Naturforchenden Gesellschaft in Danzig,” 1843, goes over the whole subject, and is particularly useful on the sexual habits. The same author continues the subject in “Preussische Spinnen,” published by the same society, beginning in 1866, and not yet finished. The habits of the water-spider are described by Mr. Bell in “Journal of the Linnæan Society,” 1857. The trap-door spiders and their habits are described by J. T. Moggridge in “Harvesting Ants and Trap-door Spiders,” published by L. Reeve & Co., London, 1873, and Supplement, 1874. Prof. B. G. Wilder has published several papers on the habits of American spiders, the most useful of which are the following: on Nephila plumipes from South Carolina, “Proceedings of the Boston Society of Natural History,” 1865; Practical Use of Spider’s Silk in “The Galaxy,” July, 1869; Habits of Epeira riparia, Moulting of Nephila plumipes, and Nests of Epeira, Nephila, and Hyptiotes, in “Proceedings of American Association for Advancement of Science,” 1873; the Triangle Spider in “Popular Science Monthly,” 1875.

INDEX.

Abdomen, 12, 16. Adhesive threads, 67. Adult characters of spiders, 87. Agalena, web of, 55. Agalenidæ, 26. Age of spiders, 112. Air-sacs, 22. Air-tubes, 12. Anyphena, flying of, 84. Argiope, web of, 67. Argyrodes, 58. Attidæ, 28. Attus, flying of, 85.

Bertkau, experiments on poison of spiders, 34. Blackwall, age of spiders, 112; experiments on poison, 35; on blowing out of threads, 80; on flying spiders, 82. Blind spiders, 113. Blowing of threads, 80. Breathing-organs, 16, 22.

Calamistrum, 73. California trap-door spider, 49. Care of young, 104. Cave spiders, 113. Ciniflonidæ, 72. Classification of spiders, 11, 23. Claws, 14. Cobwebs, 54. Cocoons, 98. Colors of spiders, 17, 19. Concealment of spiders, 70. Copulation, 94. Crab spiders, 29. Cribellum, 72. Curled webs, 72.

Darwin on flying spiders, 83. Dictyna, spinning of, 73; regular webs of, 74. Distribution of spiders, 113. Doleschall, experiments on poison of spiders, 34. Dolomedes, nest for young, 53. Dorsal groove, 17. Drassidiæ, 26.

Eggs, laying, 98; growth of, 105. Embryo spiders, 105. Epeiridæ, 31. Epigynum, 92. Erigone, heads of male, 88. Eyes, 17.

Feet, 14. Flying of spiders, 79. Food of trap-door spiders, 50.

Growth of spiders, 86.

Habitats of spiders, 113. Hatching, 107. Heads of male spiders, 88. Heart, 21. Hoisting captured insects, 60. Holes, 44. House spiders, 114.

Intestine, 21.

Jumping spiders, 28.

Laying eggs, 98. Legs, 14. Linyphia communis, web of, 58. Linyphia marmorata, web of, 58. Lycosa, flying of, 81. Lycosidæ, 27.

Mandibles, 33. Maxillæ, 15. Moggridge, on poison of spiders, 36; on trap-door spiders, 46. Moulting, 110. Mouth, 59. Mygalidæ, 23.

Nephila, web of, 66. Nervous system, 22. Nests, 52. Noise by a spider, 16.

Œsophagus, 19.

Palpi, 14. Palpal organs, 89. Parasitic spider, 58. Parasites of spiders, 104. Pholcus, habit of, when frightened, 61. Poison of spiders, 34. Poison-glands, 23.

Regular web of Dictyna, 74. Repair of webs, 67. Reproduction, 94. Reproductive organs, 22. Round webs, 61. Running spiders, 27.

Saunders, S. S., on digging of trap-door spiders, 50. Sexes of spiders, 86. Shooting of threads, 79. Six-eyed spiders, 25. Shaking web when frightened, 70. Spines, 14. Spinnerets, 39, 41. Spinning-glands, 40. Spinning-tubes, 40. Spots on top of abdomen, 17. Stomach, 21. Sucking-stomach, 19.

Tame spiders, 37. Tarantula, 36. Theridion, web of, 60. Theridiidæ, 30. Thomisidæ, 29. Thorax, 12. Thread, 38, 42. Tracheæ, 17. Trap-door nests, 44. Triangle spider, 75. Tubes, 52. Tying up insects, 43.

Use of spider’s web, 70.

Water spider, 53. Wilder, on moulting of spiders, 110; Triangle spider, 75; use of spider’s silk, 70. Winter habits of spiders, 113.

Young spiders, 107; escape from cocoon, 103.

Zilla, web of, 65.

_Electrotyped by C. J. Peters & Son, Boston, Mass._

Transcriber’s Notes:

Underscores “_” before and after a word or phrase indicate _italics_ in the original text. Small capitals have been converted to SOLID capitals. The illustrations have been moved so they do not break up paragraphs. Typographical errors have been silently corrected but other variations in spelling and punctuation remain unaltered.