formed of a compact, horizontal sheet of web, with a tube of greater or less dimensions at or
near one of its margins, from which several lines frequently extend along its upper surface to
the other margins, where they become attached. A fourth presents the appearance of an
irregular web of white or bluish silk, the tortuous filaments of which have been curled and
inflected by the calamistra before described; in this snare one or two funnel-shaped tubes
usually occur. The most elegant snares, however, are those constructed with the appearance
of geometrical precision in the form of circular nets. They are composed of an elastic spiral
line, thickly studded with minute globules of liquid gum, whose circumvolutions, falling within
the same plane, are crossed by radii converging towards a common centre, which is immediately
surrounded by several circumvolutions of a short, spiral line, devoid of viscid globules,
forming a station from which the toils may be superintended by their owner without the
inconvenience of being entangled in them. As the radii are unadhesive, and possess only a
moderate share of elasticity, they must consist of a different material from that of the viscid,
spiral line, which is elastic in an extraordinary degree. Now, the viscidity of this line maybe
shown to depend entirely upon the globules with which it is studded, for if they be removed
by careful applications of the finger, a fine, glossy filament remains, which is highly elastic,
but perfectly unadhesive. As the globules, therefore, and the line on which they are disposed,
differ so essentially from each other and from the radii, it is reasonable to infer that the
physical constitution of these several portions of the net must be dissimilar.
An estimate of the number of viscid globules distributed on the elastic, spiral line in a
net of Epeira apoclisa of a medium size, will convey some idea of the elaborate operations
performed by the Epeira in the construction of their snares. The mean distance between two
adjacent radii, in a net of this species, is about seven tenths of an in ch ; if, therefore, the
number .seven be multiplied by twenty, the mean number of viscid globules which occur on
one tenth of an inch of the elastic spiral line, at the ordinary degree of tension, the product will
be 140, the mean number of globules deposited on seven tenths of an inch of the elastic,
spiral line; this product multiplied by twenty-four, the mean number of circumvolutions
described by the elastic spiral line, gives 3360, the mean number of globules contained
between two radii; which, multiplied by twenty-six, the mean number of radii, produces 87,360»
the total number of viscid globules in a finished net of average dimensions. A large net,
fourteen or sixteen inches in diameter, will be found, by a similar calculation, to contain
upwards of 120,000 viscid globules, and yet Epeira apoclisa will complete its snare in about
forty minutes if it meet with no interruption.1
In the formation of their snares the Epeira appear to be regulated solely by the sense of
touch, as various species, when confined in spacious glass jars placed in situations absolutely
impervious to light, construct nets which do not exhibit the slightest irregularity of plan or defect
of structure.
Dr. Lister supposed that spiders are able to retract the lines they spin within the
abdomen, and whoever minutely observes the Epeira, when fabricating their snares, will almost
be induced to entertain the same opinion. The viscid line produced by these spiders in their
transit from one radius to another, is sometimes drawn out to a much greater extent than is
necessary to connect the two, yet on approaching the point at which it is to be attached, it
1 ( Transactions of the Linnean Society/ vol. xvi, pp. 477-479.
appears to re-enter the spinners, till it is reduced to the exact length required. This optical
. illusion, for such it is, is occasioned by the extreme elasticity of the line, which may be
extended greatly by the application of a slight force, and on its removal will contract proportionally.
By this property the viscid, spiral line is accommodated to the frequent and rapid
changes in distance .which take place among the radii when agitated by winds or other
disturbing forces, and by it insects, which fly against the snare, are more completely entangled
than they otherwise could be without doing extensive injury to its framework.
Complicated as the processes are by which these symmetrical nets are produced,1 nevertheless
young spiders, acting under the influence of instinctive impulse, display, even in their
first attempt to fabricate them, as consummate skill as the most experienced individuals.
By contributing to check the too rapid multiplication of insects, from which they chiefly
derive their sustenance, spiders^ perform an important part in the economy of nature. They
devour one another also, the weaker falling victims to the more powerful ; and as female
spiders, with few exceptions, are larger and more vigorous than males, they frequently prey
upon the latter, sometimes, indeed, immediately after they have received their embraces.
Their enemies, however, are not limited to those of their own kind; quadrupeds, birds, fishes,
reptiles, and even insects, destroy them in large numbers.
Although spiders are not provided with wings, and, consequently, are incapable of flying,
in the strict sense of the word, yet, by the aid of their silken filaments, numerous species,
belonging to various genera, are enabled to accomplish distant ( journeys through the
atmosphere. These aerial excursions, which appear to result from an instinctive desire to
migrate, are undertaken when the weather is bright and serene, particularly in autumn, both
by adult and immature individuals, and are effected in the following manner. After climbing to
the summits of different objects, they raise themselves still higher by straightening the limbs ;
then elevating the abdomen, by bringing it from the usual horizontal position into one almost
perpendicular, they emit from the spinners a small quantity of viscid fluid, which is drawn out
into fine lines by the ascending current occasioned by the rarefaction of the air contiguous to
the heated ground. Against these lines the current of rarefied air impinges, till the animals,
feeling themselves acted upon with sufficient force, quit their hold of the objects on which they
stand and mount aloft.
Spiders do not always ascend into the atmosphere by a vertical movement, but are
observed to sail through it in various directions; and the fact admits of an easy explanation
when the disturbing causes by which that subtile medium is liable to be affected are taken
into consideration. A direction parallel to the horizon will be given by a current of air moving
in that plane; a perpendicular one, by the ascent of air highly rarefied; and directions intermediate
between these two will, in general, depend upon the composition of forces. When
the horizontal and vertical currents are equal in force, the line of direction will describe an
angle of 45° nearly with the plane of the horizon; but when their forces are unequal,
the angle formed with that plane will be greater or less as one current or the other
predominates.
The manner'in which the lines are carried out from the spinners by a current of air
appears to be this. As a preparatory measure, the spinning mammulae are brought into close
1 c Zoological Journal/ vol. v, pp. 181-188. ‘ Researches in Zoology/ pp. 253-270.