ir4 



THE CABINET OF NATURAL HISTORY 



shapes and dimensions, some of the largest measuring up- 

 wards of a yard in lengtli, 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 positiiui 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 afibrding 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 agencj^ 

 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 i^ 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 



