340 



FOOD OF INSECTS. 



others, and furnished a larger thread. Thus a spider's thread, 

 even spun by the smallest species, and when so fine that it is 

 almost imperceptible to our senses, is not, as we suppose, a 

 single line, but a rope composed of at least four thousand 

 strands.^ But to feel all the wonder of this fact we must 

 follow Leeuwenhoek in one of his calculations on the subject. 

 This renowned microscopic observer estimated that the 

 threads of the minutest spiders, some of which are not larger 

 than a grain of sand, are so fine that four millions of them 

 would not equal in thickness one of the hairs of his beard — 

 a tenuity utterly beyond the power of the imagination to 

 conceive. Of the probable accuracy of this calculation, you 

 may any day in summer convince yourself, by taking one of the 

 large diadem spiders (Epeira Diadema), and, after pressing 

 its abdomen against a leaf or other substance, so as to attach 

 the threads to the surface — the same preliminary step which 

 the spider adopts in spinning — drawing it gradually to a 

 small distance. You will plainly perceive that the proper 

 thread of the spider is formed of four smaller threads, and 

 these again of threads so fine and numerous, that there cannot 

 be fewer than a thousand issue from each spinner ; and if 

 you pursue your researches with the microscope, you will 

 find that precisely the same takes place in the minutest 

 species that spins. You will inquire what can be the end of 

 machinery so complex ? One probable reason is, that it was 

 necessary for drying the gum sufiftciently to form a tenacious 

 line, that an extensive surface should be exposed to the air, 



1 Mr. Blackwall, however, as the result of his examinations with micro- 

 scopes of high powers, denies that spiders' threads are composed of so many fine 

 lines as Leeuwenhoek, I^yonnet, Treviranus, &c., have supposed. He has not, 

 lie says, found that any lines ever issue, as they describe, from the minute aper- 

 tures without projecting margins, situated between the papillae or spinning tubes, 

 which last alone he regards as the sole line-forming instruments, and the total 

 number of these in the larger adult species of Epeira, which are best provided 

 with them, he does not estimate at much above a thousand, while in the common 

 house-spider they are below four hundred, and in other species not above one 

 hundred, and in some much fewer. As the statements of such careful and gene- 

 rally accurate observers as Reaumur, DeGeer, Leeuwenhoek, Lyonnet, Treviranus, 

 and other eminent naturalists, all in the main agreeing and confirming each other, 

 ought not to be hastily set aside and without the fullest investigation, it has been 

 thought best, without materially altering the text, simply to point out in the pre- 

 sent note Mr. Blackwall's different conclusions, and to refer the reader for the 

 details on which they rest to his paper on the Mammulae of Spiders in the l^th 

 vol. of the Linnean Transactions, p. 219. 



