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.
[Illustration: Fig. 43.]
[Illustration: Fig. 44.]
[Illustration: Fig. 45.]
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.
[Illustration: Fig. 46.]
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.
[Illustration: Fig. 47.]
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.
[Illustration: Fig. 48.]
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.
[Illustration: Fig. 49.]
[Illustration: Fig. 50.]
[Illustration: Fig. 51.]
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.
[Illustration: Fig. 52.]
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.
[Illustration: Fig. 53.]
[Illustration: Fig. 54.]
[Illustration: Fig. 55.]
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.
[Illustration: Fig. 56.]
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.
[Illustration: Fig. 57.]
[Illustration: Fig. 58.]
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.
[Illustration: Fig. 59.]
[Illustration: Fig. 60.]
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.
[Illustration: Fig. 61.]
[Illustration: Fig. 62.]
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.
[Illustration: Fig. 63.]
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_.
[Illustration: Fig. 64.]
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.
[Illustration: Fig. 65.]
_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.
[Illustration: Fig. 66.]
[Illustration: Fig. 67.]
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.