Encyclopaedia Britannica > Volume 3, Anatomy-Astronomy

A R A C H
Arach- the air was liable to be sensibly agitated: I resolved there-
nides. fore to put a bell glass over them, and in this situation
they remained 17 days, evidently unable to produce a
single line by which they could quit the branch they
occupied, without encountering the water at its base;
though, on the removal of the glass, they regained their
liberty with as much celerity as in the instances already
recorded.” {Linn. Trans. voL xv.) Mr Blackwall affirms
with confidence, that in motionless air, spiders have not
the power of darting their threads even through the space
of half an inch. Mr Murray, Mr Bowman, Mr Mark
Watt, and others, maintain a contrary opinion.
Lastly, Mr Virey thinks it more probable that spiders
actually fly (by vibrating their feet) through the air,
than that they are acted upon either by electrical influ¬
ences or the agitation of the air. He does not assert that
they have wings.
The bodies of spiders decompose so rapidly after death,
that both their forms and colours are speedily altered
and effaced. It is therefore with great difficulty that
they are preserved as subjects of examination in mu¬
seums. Hence, perhaps, our comparative ignorance both
of their structure and habits.
Sect. I.—Tetrapneumones.
Two spiracles and two pulmonary sacks or pneumo-
branchia on each side.
This section is characterized by the position of the eyes,
which are always placed at the anterior extremity of the
thorax, and usually close to each other. The mandibles
{cheliceres of Latreille) and feet are robustly formed. The
greater proportion of species have only four spinners.
They fabricate silken tubes, in which they dwell, and
these are placed sometimes in subterranean tunnels,
sometimes under stones, and sometimes beneath the bark
or among the leaves of trees.
The first division of the section corresponds to the
Theraphoses of Walckenaer, and contains the three fol¬
lowing genera, viz. Mygale, Atypus, and Erodion. These
are distinguished from the others by having four spinners
and eight eyes, and by the hooks of their mandibles be¬
ing bent underneath instead of inwards.
Genus Mygale, Walckenaer.—Palpi inserted at the su¬
perior extremity of the maxillse, in such a manner that
they appear to be composed of six articles, of which
the first, straight and elongated, with the inner angle
of its upper portion projecting, performs the function
of a jaw. The languette is small and nearly square.
The last joint of the palpi in the male is button-shaped,
and bears at its extremity the reproductive organs ; and
the two anterior legs in that sex are provided with two
strong spines or spurs at their inferior extremity.
This genus, as established by Walckenaer, is composed
of the bird-catching spiders (A. avicularia, Linn.), and the
Araignees mineuses of Olivier. It contains several species of
great size and singular habits. The foreign kinds are as
yet imperfectly characterized. The habits of a large spe¬
cies found in Martinique, where it is called Matoutou, have
been well described by Moreau de Jonnes. It spins no
web, but lies concealed in holes and crevices of the vol¬
canic tufa, from which, however, it makes frequent ex¬
cursions in search of prey, which consists not only of in¬
sects, but of humming-birds and other species of the fea¬
thered race. It hunts chiefly during the night. It is
possessed of great muscular strength, and unwillingly
quits an object of which it may have become possessed.
\V hen induced to seize upon any hard and polished sub-
VOL. m.
N 1 D E S. 377
stance, it leaves traces of a poisonous liquid, which, had Arach-
the substance been of a yielding nature, it would have in- nides.
jected into the wound. This liquid is lactescent, or of a
milky aspect, and very abundant in proportion to the size
of the animal. I he female carries her eggs in a cocoon
of white silk, of a very close texture, which she holds by
means of her palpi, beneath the thorax. When attacked,
she drops her eggs to defend herself, and secures them
again when the combat has ceased. The young, when
first produced, are entirely white ; and the earliest change
which they experience is the appearance of a black spot
in the centre of the dorsal surface of the abdomen. From
eighteen hundred to two thousand young have been ob¬
served to proceed from a single silk bag; but of these it
is probable that an immense proportion perish in infancy,
by the depredations both of birds and insects.
Several species of this genus inhabit Europe, and their
characters and economy are detailed by Olivier, Latreille,
the Abbe Sauvage, and other writers. Our restricted
limits prevent our describing more than a few, which we
shall select as well from the indigenous as exotic.
f Superior extremity of the mandibles unprovided with
a series of transverse spines or corneous points.
Tarsi furnished with a thick hairy brush, which
conceals the crotchets.
Sp. Avicularia.—Aranea Avicularia, Linn. The bird-
catching spider, Shaw. (PI. XLVI. fig. ])—Body nearly
two inches long, very hairy, especially in the young. Tho¬
rax depressed, large, oval, truncated posteriorly. Ge¬
neral colour black; the extremities of the palpi, the
feet, and inferior hairs of the mouth, reddish. Hooks
of the mandibles strong, conical, and very black. This
species is said to dwell in the clefts of trees, and in hol¬
lows among rocks and stones. According to Madame
Merian, it surprises small birds on their nests, and sucks
their blood with avidity. It forms a tube-shaped cell,
narrow at its posterior extremity, composed of a fine white
semi-transparent tissue, resembling muslin. The cocoon
of this species is like a large walnut in size and form.
Its native countries are Cayenne and Surinam. Other
nearly allied species also occur in those parts of South
America, as well as in Africa and the East Indies. Their
bite is dangerous, although the accounts given by Piso
and other authors is no doubt exaggerated. To this sec¬
tion may be referred the M. blondi (PI. XLVI. fig. 2), can-
cerides, fasciata, atra, and brunnea of Latreille.
j-f Superior extremity of the first piece of the mandibles
provided with corneous points like the teeth of a
rake. The tarsi are not so covered with hair as to
conceal the crotchets.
The species of this section inhabit dry and mountain¬
ous places, where they form tunnels or subterranean galle¬
ries, sometimes two feet in depth. At the entrance they
construct a door, moving upon a hinge, and formed of
silk and clay, undistinguishable from the surrounding soil.
There is what we may not improperly call a mat of silk
fastened to the inner surface of the door, on which the
animal frequently reposes, probably for the sake of guard¬
ing the entrance, and being at hand to secure its passing
prey. A fine silk tube, which is the proper dwelling,
clothes the interior of the gallery. M. Dufour is of opi¬
nion that the females alone excavate the tunnels.
Sp. Cccmentaria.—Araignee mineuse, Dorthes. In
Linn. Trans, ii. (PI. XLVI. fig. 3.)—The female of this
species is about eight lines in length, of a reddish-brown
colour, somewhat pale on the edges of the thorax. Ihe
mandibles are blackish, and are each furnished near the
articulation of the crotchet with five points, of which the
innermost is the shortest. The abdomen is mouse-colour¬
ed, with darker spots. The first article of all the tarsi is