The morning news. [volume] (Savannah, Ga.) 1887-1900, 1888-07-02
SPIDER SIGHT.
Their Poor Vision-It Does Not Exceed
a Few 1nches-They See by Feeling.


According to Cosmos" Prof Plateau
has been examining the organs of sight
among the Arachnida. Their development
in this respect is far from uniform. Some,
like the scorpions, shun the daylight, and
must depend upon chance or upon their
other senses for the capture of their prey.
Others, like the majority of the true Arach-
nda, hang out snares for insects, while
other families in this group seek the light
and live by hunting. In these latter the
visual perceptions have reached the highest
grade of development.
Thanks TO the numerous eyes of the spi-
der, it is popularity credited with excellent
sight Naturaists, however, have long ago
refuted this error and shown+ that these
eyes, in virtue of their curious dimorphism
discovered by Grenacher, are very indiffer-
ent instruments. or at least that their pos
SCISSORS must be very short-sighted Muller
and Lacordaire find that spiders see dis
tinctly only TO a very short distance.
Duges thinks that if a spider takes refuge
in its hole at the approach of "a man, even
at the distance of a fathom, it is not neces-
sary to suppose that it has any distinct Wis
ion at such distance, but merely recognizes
moving masses.
The researches of NJ. Plateau have not
merely confirmed these surmises, but have
extended them in an unexpected manner
His minute experiments have been extended
to various species of spiders, and have led
him to conclude that the distance at which
vision is sufficiently distinct to induce q
spider to capture It's prey is about an inch
in the most sharp-sighted species, and that
the vague perception of movements in
Epiblemum scenicum does not exceed to
inches
The following observations, which the
reader may verify in any garden on fine
day in the latter part of summer, fully con
firm the statements of NJ. Plateau If a
blue bottle falls into the web of geometri-
cal spider (Epeira diadema), she does not
rush right to the spot, but applies her feet in
rapid succession TO the radii of the web,
and thus ascertains by touch the exact posi-
ton of the struggling prey. If the web is
gently touched with a blade of grass or
soft feather she rushes TO the attack and
does not at once perceive the fraud, but
actually seizes the useless object.
We have seen a harry-long-legs get en-
tangled into a cobweb in his laundering
flight, and just manage to extricate himself
in time, leaving a leg behind him as a for
felt. The spider, hurrying up, seized the leg,
not noticing that il was bodlless, ran TO the
other end, then back to the first, only learn
ing by very close examination that the booty
was just leg, and nothing more No crea-
ture having a moderate range Of vision
could be so deceived.
The conclusions o ( M. Plateau are that
the Arachnida in general perceive the
movements OF bulky bodies from distance.
The so-called hunting spiders, such as the
LycosR, are probably the only ones which
see the movements within a range, accord
ing to some observers, at from l inch TO n
foot, but which, according 10 Plateau, docs
not exceed G inches. Even at such small
distances their sight is not distinct. Weav-
ing spiders have worry poor sight at any
distance, and only detect the presence and
the position Of their prey by the vibrations
Of the web.