174 
THE CABINET OF NATURAL HISTORY 
shapes and dimensions, some of the largest measuring up- 
wards of a yard in length, and several inches in breadth in 
the widest part; while others were almost as broad as long, 
presenting an area of a few square inches only. 
These webs, it was quickly perceived, were not formed 
in the air, as is generally believed, but at the earth’s sur- 
face. The lines of which they were composed being 
brought into contact by the mechanical action of gentle 
airs, adhered together, till by continual additions they were 
accumulated into flakes or masses of considerable magni- 
tude, on which the ascending current, occasioned by the 
rarefaction of the air contiguous to the heated ground, acted 
with so much force as to separate them from the objects 
to which they were attached, raising them in the atmos- 
phere to a perpendicular height of at least several hun- 
dred feet. I collected a number of these webs about mid- 
day as they rose, and again in the afternoon, when the up- 
ward current had ceased and they were falling, but scarce- 
ly one in twenty contained a spider; though on minute in- 
spection I found small winged insects; chiefly aphides, en- 
tangled in most of them. 
From contemplating this unusual display of gossamer, 
my thoughts were naturally directed to the animals which 
produced it ; and the countless myriads in which they 
swarmed almost created as much surprise as the singular 
occupation that engrossed them. Apparently actuated by 
the same impulse, all were intent upon traversing the re- 
gions of air; accordingly, after gaining the summits of va- 
rious objects, as blades of grass, stubble, rails, gates, &c., 
by the slow and laborious process of climbing, they raised 
themselves still higher by straightening their limbs; and 
elevating the abdomen, by bringing it from the usual ho- 
rizontal position into one almost perpendicular, they emitted 
from their spinning-apparatus a small quantity of the glu- 
tinous secretion with which they construct their webs. This 
viscous substance being drawn out by the ascending cur- 
rent of rarefied air into fine lines several feet in length, 
was carried upward, until the spiders feeling themselves 
acted upon with sufficient force in that direction, quitted 
their hold of the objects on which they stood, and com- 
menced their journey by mounting aloft. 
Whenever the lines became indequate to the purpose for 
which they were intended, by adhering to any fixed body, 
they were immediately detached from the spinners, and so 
converted into terrestrial gossamer by means of the last 
pair of legs, and the proceedings just described were re- 
peated; which plainly proves that these operations result 
from a strong desire felt by the insects to effect an ascent. 
But what, it may be asked, is the exciting cause of this 
singular propensity. It has been suggested that hunger, 
or an inclination to procure some favourite kind of food, 
may supply the requisite stimulus. These suppositions, 
however, are discountenanced by the plump appearance 
which the animals exhibit; by their total disregard of such 
winged insects as happen to be placed within their power; 
by their utter inability to regulate their motions, while 
afloat, in any other manner than by letting out or drawing 
in the lines by which they are conveyed through the air, 
and thus promoting their ascent or descent; by the unsuita- 
bleness of the lines for securing their prey; and lastly, by 
the uncertainty when a favourite day for their purpose may 
occur, or even that one may occur at all. 
Were I to hazard a conjecture on the subject, I should 
be disposed to attribute the manifest anxiety of these in- 
sects to change their quarters, to a feeling of insecurity oc- 
casioned by their proximity to one another; — the prodi- 
gious numbers which in favourable seasons are usually con- 
gregated together affording the more powerful individuals 
an opportunity, seldom neglected by these voracious crea- 
tures, of making an easy prey of the weaker: and this opi- 
nion is strengthened, if not confirmed, by the. fact, that 
they are chiefly animals which have not arrived at maturi- 
ty that undertake their migrations. 
I have asserted, that when the spiders which produce 
gossamer perform their aerial journeys, they are borne 
upward by an ascending current of rarefied air acting on 
the slender lines which proceed from their spinners. I 
shall now endeavour to prove that this curious atmosphe- 
rical phenomenon, which well deserves the attention of 
meteorologists, affords them the only available means of 
accomplishing their object; and that the hypotheses pre- 
viously adverted to are quite irreconcileable with facts, and 
consequently must be erroneous. 
It has been already stated, that gossamer is never seen 
floating in the air except in calm sunny weather; its buoy- 
ancy, therefore, evidently does not depend upon the agency 
of winds, usually so called: indeed it is probable that winds 
never do take an upward direction, unless influenced by 
some extraordinary circumstance or local peculiarity; the 
ascent of gossamer, on the contrary, is frequently observ- 
ed to take place over a great extent of country on the same 
day. It was noticed on the 1st of October, for example, 
in England, Wales, and Ireland. 
If a satisfactory explanation of this interesting fact can- 
not be derived from the operation of winds, it is still less 
likely to be deduced from the action of evaporation or elec- 
tricity; for, not to insist upon the probable, I had almost 
said absolute, insufficiency of these powers considered as 
agents, experiments show that the spiders do not select 
those periods for making an ascent when the evaporating 
