272 FOOD OF INSECTS. 



In this renewal, as above hinted, the geometrical spiders are constantly 

 regulated by the future probable state of the atmosphere, of which they 

 have such a nice perception, that M. Q. D'Isjonval, to whom we are 

 indebted for the fact, has proposed them as most accurate barometers. 

 He asserts that if the weather be about to be variable, wet and stormy, 

 the main threads which support the net will be certainly short ; but if 

 fine settled weatlier be on the point of commencing, these threads will be 

 as invariably very long.^ Without going the length, with M. D'Isjonval, 

 of deeming his discoveries important enough to regulate the march of 

 armies, or the sailing of fleets, or of proposing that the first appearance of 

 these barometrical spiders in spring should be announced by the sound of 

 trumpet, I have reason to suppose from my own observations that his 

 statements are in the main accurate, and that a very good idea of the 

 weather may be formed from attending to these insects. 



The spiders which form geometrical nets differ from the weavers also 

 with respect to the situation in which they watch for their prey. They 

 do not conceal themselves under their net, but either place themselves in 

 the centre with their head downwards, and retire to a little apartment 

 formed on one side under some leaf of a plant, only when obliged by 

 danger or the state of the weather, or, as before stated, constantly hide 

 themselves in a similar retreat. The moment an unfortunate fly or other 

 insect touches the net, the spider rushes towards it, seizes it with her fangs, 

 and if it be a small species at once carries it to her little cell, and, having 

 there at leisure sucked its juices, throws out the carcass. If the insect 

 be larger and struggle to escape, with surprising address she envelops it 

 with threads in various directions, until both its wings and legs being effect- 

 ually fastened, she carries it off to her den. If the captured insect be a 

 bee, or a large fly so strong that the spider is sensible that it is more than 

 a match for her, she never attempts to seize or even entangle it, but on 

 the contrary assists it to disengage itself, and often breaks ofi" that part 

 of the net to which it hangs, content to be rid of such an unmanageable 

 intruder at any price. — When larger booty is plentiful, these spiders seem 

 not to regard smaller insects. I have observed them in autumn, when 

 their nets were almost covered with the Aphides which filled the air 

 impatiently pulling them off and dropping them untouched over the sides, 

 as though irritated that their meshes should be occupied with such insignifi- 



gum, instead of being applied to the entire surface of the threads, should come to be divid- 

 ed in the process into distinct and bead-like globules. The subject is certainly highly 

 curious and interesting, and well deserves investigation for an additional reason originally 

 noticed above and confirmed by Mr. Blaclivvall, that the circular lines differ from the radii 

 and main lines of the net, not only in being studded with gum globules, but in being far 

 more elastic, which elasticity (as well as the vi.scidity of the gum globules) he found re- 

 mained unimpaired far more than seven months in a net of Eptira diademo consirucied in a 

 glass jar which was placed in a dark closet. (Linn. Trans, xvi. 479.) 



Before concluding this long note, an omission in the account of the geometric spiders' 

 forming their nets, in the text, which has been supplied by Mr. Blackwall, should be given, 

 namely, that in the process of spinning the concentric gummy circles, the spider, as she 

 proceeds, destroys the first made distant unadhesive circles which had served her as a scaf- 

 folding in placing the former. (Zuol. Jonrn. v. 183.) A curious calculation, also, of Mr. 

 Blackwall's, as to the number of distinct globules of gum in a geometric spider's net, 

 should be noticed. These he found to be 87,3(30 in a net of average dimensions, and 

 120,000 in a large net of fourteen or sixteen inches diameter ; and yet Eperia apoclysa will, 

 if uninterrupted, complete ils snare on an average in forty minutes, (p. 478.) 



• Brez, La Flore des Insectophiks, 129. 



i 



