FOOD OF INSECTS. 271 



from their claws becoming entangled in the fine meshes which form the 

 texture. On the other hand, the net of the garden spider is composed of 

 two distinct kinds of silk ; that of the radii not adhesive, that of the circles 

 extremely viscid.^ The cause of this difference, which, when it is con- 

 sidered that both sorts of silk proceed from the same instrument, is truly 

 wonderful, may be readily perceived. If you examine a newly formed 

 net with a microscope, you will find that the threads composing the outlme 

 and the radii are simple, those of the circles closely studded with minute 

 dew-like globules, which, from the elasticity of the thread, are easily sepa- 

 rable from each other. That these are in fact globules of viscid gum, is 

 proved by their adhering to the finger and retaining dust thrown upon the 

 net, while the unadhesive radii and exterior threads remain unsoiled. It 

 is these gummed threads alone which retain the insects that fly into 

 the net; and as they lose their viscid propeties by the action or the air, it 

 is necessary that they should be frequently renewed.^ 



* May not the spinners mentioned by Leeuwenhoek be peculiar to the retiarj spiders, 

 and furnish this viscid thread ? 



* The accuracy of the fact abovre stated as to the essential difference between the radii 

 and concentric circles from the presence of globules of gum on the latter only has been 

 denied by the amhor of Insect Architecture; but as it has been fully confirmed by Mr. 

 Blackwall, and as any one, who will examine a newly-made spider's net with a common 

 pocket lens, and throw a little du^i on it, will see for himself what is here described, it is 

 needless to refute an error that has most probably arisen from the examination of old nets, 

 which, after being exposed to wind and rain, often lose the globules of gum from the 

 circles. (F^deSpence in Loudon's Mag. of Nat. Hist. 1832, vol. v. p. 689.) 



When the writer of these letters on the food of insects, in examining tor himself the 

 whole process, from first to last, of the construction of the nets of the garden geometric 

 spider, observed this remarkable difference between the radii and concentric circles, he had 

 certainly no idea that he had made any discovery, as he never dreamed that so obvious a 

 peculiarity in objects so constantly in view had not been very frequently noticed, and even 

 described, in books, though he had not himself chanced to meet with any such description. 

 But the denial of the fact itself havuig subsequently drawn his attention to the subject, he 

 is inclined to believe (but w-ithout speaking positively on a question which he has not now 

 an opportunity of investigatmg) that the existence of these gum globules and their pecu- 

 liar object were first distinctly made known in the present work*; a circumstance, which, 

 if the fact prove to have been so, deserves being held out to the young entomologist in proof 

 how wide a field of discovery must yet remain to be explored, when points at once so curi- 

 ous and yet obvious in the economy of a spider, found in every garden, had so long re- 

 mained unnoticed. 



Another reason for directing attention to this fact is to recommend strongly to compara- 

 tive anatomists and microscopical observers an investigation of the mode in which the geo- 

 metric spiders are enabled to spin two different kinds of silk, one gummy and the other not, 

 and whether the spinners noticed by Leeuwenhoek, as suggested in a preceding note, are 

 concerned in the process — points to which Mr. Blackwall, in his examination of the spin- 

 ning apparatus of spiders {Linn. Trans, xviii. 219.), has not advened. It is obvious that 

 these spiders must either have two distinct sets of spinners, of which one spins the gummy 

 and the other the unadhesive threads, or else, if all the threads proceed from the same 

 spinners, the spider must have the means of passing the threads of the concentric circles 

 through a reservoir of gum so as to stud them with the globules of this substance which 

 give tliem their fly-catching viscidity. There is, however, a considerable difficulty in the 

 way of this last supposition, for as the threads at their issuing from the spinners are, as has 

 been already explained, so numerous, it is not easy to conceive how, after being united 

 into one, they can be passed through any gum reservoir, nor how, if they were so passed, the 



* Dr. Hooke, indeed, in a passage in his Micrographia, p. 2U2., quoted by Mr. Black- 

 wall (Linn. Trans, xvi. 479.), speaks of the radii of geometric spiders' nesis being "all 

 over knotted or pearled with small transparent globules, not unlike small crystal beads or 

 seed-pearls strung on a clew of silk ;" but, as he immediately adds, " which, whether they 

 were so spun by the spider or by the adventitious moisture of a fog (which I have observed 

 to cover all these filaments with such crystalline beads). I shall not now dispute ;" it is 

 clear that he had no distinct or correct ideas as to the origin of these globules, nor the 

 slighest conception of iheir use. 



