SPIDER. 



705 



near the extremity of the body, and the other is of 

 a poisonous nature, and flows from the mandibles. 

 With the first they are enabled to construct webs or 

 nests of various texture and form, serving for the 

 purposes of habitation, of traps for their prey, or 

 of covering for their eggs and young ; and with the 

 latter they are enabled to destroy insects larger than 

 themselves in a very short time for food. 



A very great diversity exists in the modes in which 

 the nests or webs of these insects (for we consider 

 them as such for the reasons given in our general 

 article INSECT) are constructed, and the situations in 

 which they are placed. The internal apparatus for 

 secreting the silk is lodged within the abdomen near 

 its posterior extremity, and consists of a small num- 

 ber (four or six, according to the species) of twisted, 

 elongated, and unequal-sized vessels, being thickest 

 in the middle, at the extremity of which is a great 

 number of similar vessels, but of a much smaller size, 

 and considerably shorter, and which are pressed 

 against each, uniting in a common base, which is in 

 connection with the external apparatus. The latter 

 is visible to the naked eye on the under side of the 

 abdomen, appearing, when pressed, in the shape of a 

 small star, having several small oval-shaped or sub- 

 conical appendages, teat?, or spinnerets, as we may 

 call them, placed near the extremity of the body, 

 their extremities, when at rest, being brought into 

 contact. In the greatest number of spiders there are 

 four of these spinnerets, but in some there are six, 

 two of which, however, appear to have neither pores 

 nor papillae. The matter discovered in the internal 

 vessels is analogous to a gum, or transparent paste. 

 In Epeira diadema it is of a yellow colour ; in Clu- 

 biona atrox white ; and in Aranea domestica brown. 

 It is not soluble in spirits of wine or in water ; it 

 breaks when it is attempted to be bent, and, like 

 glass, can only be made flexible when it is divided 

 into very thin threads. On examining the spinnerets 

 more minutely, it will be found that each is surrounded 

 with several series of minute bristles, like points, 

 about one thousand to each spinneret. From each of 

 these points or spinnerules is discharged a thread, so 

 that it may be easily conceived of what an immense 

 number of distinct threads the apparently simple 

 thread of the spider consists. According to a calcu- 

 lation made by Leeuwenhoeck, the celebrated micro- 

 scopist, on a young spider, not larger than a grain of 

 sand, it would require four millions of the threads 

 discharged from its spinnerules to make a cord the 

 thickness of a hair of his beard. The first object 

 which the spider has to accomplish is to attach her 

 thread to some object, as the commencement of a 

 ground-work for her future operations. In doing this 

 it appears that she extends her spinnerets as widely 

 as possible, presses them against the object to which 

 it is intended the thread should be attached, and 

 then discharges a thread from each of the spinnerules ; 

 the spinnerets are then withdrawn, and the threads, 

 by degrees, are united into a single cord ; the insect 

 uses her hind legs as a reel to draw the threads out 

 of her body. It appears, however, that the threads 

 are of different kinds ; for in the webs of the geo- 

 metric spiders those threads, which are arranged in 

 circles, are composed of more viscid materials than 

 the radii, the former being evidently intended for 

 securing the prey of the spider, and the latter serving 

 merely as its frame-work, and destitute of gluten. 

 This viscidity is produced by an immense number of 



NAT. HIST. VOL. III. 



globules of viscid matter, arranged at visible distances 

 along the elastic spiral lines of the net, and which are 

 so fluid that they run together the moment they are 

 brought into contact. Mr. Blackwall has given a 

 calculation of the number of these viscid globules in 

 the web of one of the Epeirce of a moderate size, 

 and which conveys some idea of the elaborate opera- 

 tions of the geometric spiders. The mean distance 

 between the radii in one of these nets is about 

 seven-tenths of an inch ; there are twenty viscid 

 globules on one-ten\\\ of an inch, so that there are 

 7 + 20 = 140 globules in a single line between two 

 contiguous radii seven-tenths of an inch apart ; this 

 product, multiplied by 24, being the mean number of 

 circumvolutions formed by the spiral line, will give 

 3360, being the number of globules contained on all 

 the lines between two contiguous radii ; this number, 

 being again multiplied by 26, the mean number of 

 radii, produces 87,360, the total "number of viscid 

 globules in a finished net of average dimensions. 

 But larger nets, by a similar calculation, will contain 

 upwards of 120,000 viscid globules, and yet the time 

 occupied in the construction of this net is not more 

 than forty minutes. Moreover, the threads with 

 which the spider composes the retreat in which it 

 takes up its abode, or the nest in which it envelopes 

 its young, does not appear to be of the same nature 

 as the net-threads, neither are the threads of which it 

 forms the case for its eggs similar to the former, the 

 texture of these cases being in some species quite 

 firm and smooth, resembling parchment. This case 

 is also sometimes covered with a coating of loose 

 flossy silk, which also seems of a different texture ; 

 hence it is evident that the vessels at the extremity of 

 the abdomen, which serve for the secretion of the 

 silk, as well as the structure of the spinnerets and 

 spinnerules, require a much more minute investiga- 

 tion than has hitherto been given to them, in order to 

 discover the precise manner in which these various 

 kinds of silk are elaborated and discharged. 



The nest of Epeira diadema is one of the most 

 beautiful and most common of the spider construc- 

 tions in this country, being found in every bush or 

 tree, between hedges and shrubs, &c., during the 

 autumnal months. The top line of this web appears 

 to be first spun, either by attaching a thread as above 

 described, and then earn ing it along until it is of suffi- 

 cient length, when it is attached to some adjacent 

 object to which the spider has crawled, or by throw- 

 ing out a floating line, whilst the spider remains 

 stationary, the action of the air carrying this line on 

 until it becomes attached to some object, when, in 

 either case, it is doubled and redoubled, until it is of 

 sufficient strength to bear the weight ot the intended 

 fabric, together with the spider itself. The other outer 

 threads of the frame-work are then added, and then a 

 cross line is carried from one point of the web to 

 another exactly opposite. From the middle of this 

 cross line the insect ascends or descends, having first 

 glued another thread at the centre, which she draws 

 out until she reaches the frame-lines, and then, going 

 along the latter to a certain distance, she fastens the 

 thread which she has been spinning to one of the 

 frame-lines. In this manner she constructs a com- 

 plete series of spokes or radii, which she then attaches 

 together by a spiral series of transverse bars of a more 

 glutinous thread, as above noticed. In spinning this 

 spiral \veb she first attaches a thread to one of the 

 radii, and then drawing it out with her hind legs, 

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