On the aerial excursions of Spiders. 15§ 



Commissioners, to turn his attention to the subject, and to make various 

 experiments on different kinds of wood submerged at the same place, with 

 the view of learning their mode of boring, and if possible to discover some ' 

 means by which the contemplated erection might be secured from their 

 depredations. We are not aware that any thing has been discovered, fur- 

 ther than the necessity of covering that part of the piles under water by 

 a casing of metal. Reports on the subject from three learned professors in 

 this University were, it is understood, procured by Mr Day, which there is 

 no doubt will have conveyed all the known information regarding the 

 animal, its habits, ami the best mode of securing submerged wooden 

 work from its depredations ; and it would be desirable that the results of 

 their recommendation were generally known, as the animal seems to be 

 pretty generally diffused. 



The animal was ascertained by Mr Stark to be the Limnoria terebrans 

 of Dr Leach, and which was first described by that gentleman from spe- 

 cimens sent him by Mr Stevenson in wood from the Bell Rock Light- 

 House. It is a very small crustaceous animal, about three lines long, and makes 

 the perforations which are so destructive to submerged wood-work merely 

 as places of retreat. From the observation of the living animal by Pro- ; 

 fessor Grant it does not appear to feed on the ligneous matter. 



4. On the means by which Spiders that produce Gossamer effect their 



aerial excursions. By J. Blackwall, Esq. 

 The following interesting abstract of a paper on this subject read at the 

 Linnaean Society, is given in the Philosophical Magazine for August. 



'' After noticing, that, in the absence of accurate observation, the ascent 

 of gossamer spiders through the atmosphere had been conjecturally ascribed 

 to several causes, such as the agency of winds, evaporation, electricity, or 

 some peculiar physical powers of the insect, or from their webs being 

 lighter than the air, Mr Blackwall states that the ascent of gossamers takes 

 place only in serene bright weather, and is invariably preceded by gossa- 

 mers on the ground. He then details the phenomena of a remarkable 

 ascent of gossamers, October 1, 1826, when, a little before noon the ground 

 was every where covered with it, the day being calm and sunny. A vast 

 quantity of the fine shining lines were then seen in the act of ascending, 

 and becoming attached to each other in various ways in their motions, and 

 were evidently not formed in the air but on the earth, and carried up by 

 the ascending current caused by the rarefaction near the heated ground ; 

 and when this had ceased in the afternoon they were perceived to fall. 

 An account is added of two minute spiders that produced gossamer, and 

 of their mode of spinning; and particularly when, impelled by the desire 

 of traversing the air, they climb to the summits of varicus objects, and 

 thence emit the viscous threads in such a manner as that it may be drawn 

 out to a great length and fineness by the ascending current, until, feeling 

 themselves sufficiently acted upon by it, they quit hold of the objects on 

 which they stood, and commence their flight. Some of these insects,, 

 which were taken for the purpose of observation, when exposed to a slight 



