KIO P L A T A . Dec. 1833. Dec. 1833. .AERONAUT S P ID E R S .
has been observed by Strack ; may it not be in consequence
of the little insect having passed through a dry and rarefied
atmosphere ? Its stock of web seemed inexhaustible. While
watching some that were suspended by a single thread, I
several times observed that the slightest breath of air bore
them away out of sight, in a horizontal line. On another
occasion (25th) under similar circumstances, I repeatedly
observed the same kind of small spider, either when placed, or
having crawled, on some little eminence, elevate its abdomen,
send forth a thread, and then sail away in a lateral course,
but with a rapidity which was quite unaccountable. I thought
I could perceive that the spider before performing the above
preparatory steps, connected its legs together with the most
delicate threads, but I am not sure, whether this observation
is correct.
One day, at St. Fe, I had a better opportunity of observing
some similar facts. A spider which was about three-tenths
of an inch in length, and which in its general appearance
resembled a Citigrade (therefore quite different from the
gossamer), while standing on the summit of a post, darted
forth four or five threads from its spinners. These glittering
in the sunshine, might be compared to rays of
ligh t; they were not, however, straight, hut in undulations
like a film of silk blown by the wind. They were more
than a yard in length, and diverged in an ascending direction
from the orifices. The spider then suddenly let go its hold,
and was quickly borne out of sight. The day was hot and apparently
quite calm; yet under such circumstances the atmosphere
can never be so tranquil, as not to affect a vane so delicate
as the thread of a spider’s web. If during a warm day we
look either at the shadow of any object cast on a bank, or over
a level plain at a distant landmark, the effect of an ascending
current of heated air will almost always be evident. And this
probably would be sufficient to carry with it so light an object
as the little spider on its thread. The circumstance of spiders of
the same species but of different sexes and ages, being found
on several occasions at the distance of many leagues from the
land, attached in vast numbers to the line.s, proves that they
are the manufacturers of the mesh, and that the habit of sailing
through the air, is probably as characteristic of some tribe,
as that of diving is of the Argyroneta. We may then reject
Latreille’s supposition, that the gossamer owes its origin to
the webs of the young of several genera, as Epeira or Thomisa:
although, as we have seen that the young of other spiders do
possess the power of performing aerial voyages.*
During our different passages south of the Plata, I often
towed astern a net made of bunting, and thus caught many
curious animals. The structure of the Beroe (akind of jelly
fish) is most extraordinary, with its rows of vibratory ciliic,
and complicated though irregular system of circulation. Of
Crustacea, there were many strange and undescribed genera.
One, which in some respects is allied to the Notopods (or
those crabs which have their posterior legs placed almost
on their backs, for the purpose of adhering to the under
side of ledges), is very remarkable from the structure of its
hind pair of legs. The penultimate joint, instead of being
terminated by a simple claw, ends in three bristle-like
appendages of dissimilar lengths,—the longest equalling that
of the entire leg. These claws are very thin, and are serrated
with teeth of an excessive fineness, which are directed
towards the base. The curved extremities are flattened, and
* I was n o t a t th e tim e aw a re o f M . V ir e y ’s v e ry c u rio u s o b s e rv a tio n s ,
(B u lle tin des Scien ces N a tu r ., tom . x ix ., p . 1 3 0 ) w h ic h se em to p ro v e th a t
sm a ll sp id e rs , in a n a tm o s p h e re p e rfe c tly tr a n q u il, a n d w i th o u t th e a id o f
a n y web, h a v e th e p ow e r o f d a rtin g th ro u g h th e a ir . M . V irey , b e lie v e s
t h a t b y m ea n s o f a r a p id v ib ra tio n o f th e i r f e e t, th e y walk the air.
A ith o u g li in liis case, th e co n c lu s io n seem s a lm o s t in e v itab le , y e t in tlie
o n e I h av e d e scrib ed , w e m u s t s u p p o s e t h a t th e s e v era l th re a d s w h ic h w e re
s e n t fo rth , s e rv e d as sails fo r th e a tm o s p h e ric c u rr e n ts to a c t o n . A f te r
re a d in g M. V irey ’s a c co u n t, i t a p p e a r s to m e fa r from im p ro b a b le , th a t
th e l it tl e a e ro n a u t a c tu a lly d id u n ite , as w a s su sp e c te d , its f e e t to g e th e r
b y som e fine lin e s ; th u s fo rm in g a rtific ia l wings. I r e g r e t I d id n o t d e te
rm in e tliis p o in t w ith a c cu ra c y ; fo r i t w o u ld b e a c u rio u s fac t, t h a t a
sp id e r s h o u ld th u s b e a b le to t a k e flig h t b y th e a id o f t em p o r a ry wings.
I A '