1 86 Mr. Blackwall's Observations on Aeronautic Spiders. 



To obviate such objections as might be urged against the 

 use of glass or glazed earthen vessels by the advocates of the 

 electrical hypothesis of the ascent of spiders, I have in many 

 instances employed polished vessels of silver, tin, iron, &c. 

 without producing the least difference in the results. I am 

 not ignorant that these results have been represented as abso- 

 lutely subversive of my views. Spiders, it is argued, are co?n- 

 pelled to dart out their threads by the electrical excitation 

 occasioned by currents of air, the phaenomenon being con- 

 sidered inexplicable on any other principle whatever ; but it is 

 not found expedient to assign a reason for this sudden con- 

 version of the power ascribed to these animals of propelling 

 their lines to a distance, into a merely involuntary action en- 

 tirely dependent upon air in motion. The fallacy of the fore- 

 going supposition may be proved by placing spiders of the 

 same species on copper rods insulated by water, and subject- 

 ing them to the influence of a stream of air so slight as scarcely 

 to be perceptible. Under such circumstances, any electricity 

 induced in the spiders by the feeble current must be carried 

 away as speedily as it is excited, by so excellent a conductor 

 as copper; nevertheless, the animals can emit or retain their 

 liquid gum at pleasure, as lines may frequently be seen stream- 

 ing from the papillas of some individuals ; while others, on the 

 same rod, do not let out any, and may be instantly diverted 

 from their purpose, should they make the attempt, by the 

 most trifling causes of disturbance. It is manifest, therefore, 

 that spiders do not fly, in the strict sense of the word ; and 

 that they are not raised into the atmosphere by the agency 

 of electricity is equally evident; in short, not a doubt can be 

 entertained by those whose minds are open to conviction, that 

 their ascents are effected by means of upward currents of air 

 impingeing against the lines which proceed from their papillse. 



The two species of aeronautic spiders, whose proceedings 

 are detailed in the Linnean Society's Transactions, vol. xv. 

 part ii., I have ascertained to be Thomisus cristatics and Ijycosa 

 saccata, both of which are distinctly mentioned as aeronautic 

 spiders by Dr. Lister*. The first I have desci'ibed as having 

 two pair of eyes situated in the anterior part of the head and 

 arranged thus, *. .• ; the second as having three pair in front 

 whose arrangement is thus represented by dots .*. .*. . 'I'he 

 species noticed in my paper as remarkable for the skill it dis- 

 played in spinning its way up the sides of a phial in which it was 

 confined, and for having existed seventy-five days without 

 food or moisture, was T. ci-istatus; L. saccata being neither so 



• De Araneis, p. 79, 80, 85. 



expert 



