352 



FOOD OF INSECTS. 



of silk ; that of the radii not adhesive, that of the circles ex- 

 tremely yiscid.^ The cause of this difference, which, when it 

 is considered that both sorts of silk proceed from the same in- 

 strument, 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 outline 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 separable from each other. That these are in fact glo- 

 bules 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 properties by the action of the 

 air, it is necessary that they should be frequently renewed.'-^ 



1 May not the spinners mentioned by Leeuwenhoek be peculiar to the retiary 

 spiders, and furnish this viscid thread ? 



2 The accuracy of the fact above 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 author 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 dust 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. 

 (^Vide Spence 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 for him- 

 self 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 having subsequently drawn his attention to the subject, he is in- 

 clined to believe (but without speaking positively on a question which he has 

 not now an opportunity of investigating) that the existence of these gum glo- 

 bules and their peculiar 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 



* Dr. Hooke, indeed, in a passage in his Micrographia, p. 202., quoted by 

 Mr. Blackwall (Linn. Trans, xvi. 479.), speaks of the radii of geometric spiders* 

 nests 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 fila- 

 ments 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 slightest 

 conception of their use. 



