632 



SPIDKKS 



really hear, and it may be that careful experiments 

 will prove that what are described at) 'auditory 

 hairs on the palps and legs are really such. The 

 Miwe of smell seems to be slight, though marked 

 for certain strongly -scented substances, and there 

 is a sensory structure, perhaps olfactory or gusta- 

 tory, on the basal joint of the padiaaipl 



All spiders arc predaceous and feeu on insects, 

 which they entangle in their snares and webs, or 

 stalk, or catch after patient lurking. In most 

 cases they kill their prev with their poisonous 

 falees. Tlic mouth is small, and behind the gullet 

 t here is a powerful suctorial region which acts as a 

 suction-pump. From the mid-gut five paired out- 

 growths extend into the bases of the pcdi palps and 

 legs. There are also large tubular digestive out- 

 growths, and two excretory Malpigliian tubes 

 grow out from the hind gut. Tne heart lies 

 dorsally in the alxlomen, and has three chambers 

 with three pairs of valved openings. In one set 

 (Tetrapneumones, e.g. the bird-catching Mygale ; 

 see HiRD-CATCHlXG SPIDER) there are four pul- 

 monary sacs like those of the scorpion ; in the 

 great majority ( Dipneumones) there are two pul- 

 monary Macs and two main trachea) tubes. 



The" sexes are separate except in a few casual 

 hermaphrodites, and the males are often fewer in 

 number, always smaller in size, and usually more 

 brightly coloured than the females. In inu-i 

 cases, as we shall afterwards see, the courtship is 

 elaborate, and is often attended with considerable 

 danger to the males. The fertilised egg segments 

 peripherally, like that of insects, around a central 

 core of yolk. A cocoon is usually formed around 

 the eggs, and this is hidden or carried about by 

 tin- female, who exhibits much maternal solicitude. 



The fertility of spiders varies in different species 

 within wide limit-. Thus, as Mrs Peckham notes, 

 one species may lay 800 or 1000 eggs, while an- 

 other, eijii.-illv common, lays only fifty. In the 

 family Epeiridne Argiope cophiiutria fays 500 to 

 2200 eggs, while Tetraynatfia laboriota "lays only 



34 ; in the family Attidiu Phulipput morsitans lavs 

 about 180 eggs, while Synagetes perata lays only 

 three. While the rate of multiplication is imme- 

 diately dependent on the constitution of the differ- 

 ent -p.-cie-. it also bears some relation to the rate 

 of mortality, or, what comes almost to the same 

 thing, to the efficiency of the protective adapta- 

 tions by which spiders are saved from their ene- 

 mies. "Those with a low birth-rate are usually 

 protected very efficiently, and have consequently a 

 low rate of mortality. 



In many cases female spiders are savage and 

 quarrelsome, fighting with one another, and fre- 

 quently destroying the smaller males when these 

 offer them amatory attentions. ' Ridiculously 

 small and weak in build, the males of many species 

 can only conduct the rites of marriage with their 

 enormous ami voracious brides by a process of 

 active manoeuvring, which, if unsuccessful, i* 

 certain to cost them their lives." In a gn-ai 

 number of cases, e.g. in at least two-fifths of all 

 the species of Attidie, the males are more bril- 

 liantly coloured than the females, and that this is 

 in part related to sexual selection is rendered almo-t 

 certain by the observations of professor ami Mrs 

 Peckham, who often worked four or live hours a 

 day for a week in getting a fair idea of the habits 

 of a single species. They describe among many 

 species of Attidie the manner of the wooing, the 

 cautions circling dances of the ardent males, the 

 strange attitudes by whii-li they di-pla\ I heir charms 

 of colour, the occasional wooing by vibrations of 

 the web-lint-*, the captious irritability of the 

 females, who often bring the courtship to a tragic 

 end. the quarrelsomeness of rival males in presence 

 of the females. 'The males vie with each other 



?*(" r itta **> 

 n ' mle d">l'l>'ing hi* 



'"? w .,, 

 ( 



in making an elaborate display, not only of their 



grace ami agility but also of their beauty, before 



the females, who, after at ten 



lively watching the dances 



and tournamenU which have 



been executed for their grati- 



fication, select for their mates 



the males which they find 



most pleasing' (see SEXUAL 



SKi.K(-npN). 



X/itituing-icork.On each 

 of the spmnerete of which 

 in the majority there are six 

 there are numerous, usu- 

 ally sixty to seventy, 'spin- 

 ning-spools,' out of which 

 there flows a viscid secretion 

 formed in the numerous in- 

 tei nal glands. The resultant 

 thread into which the secre- 

 tion hardens, though of a delicacy hardly rivalled 

 except by quartz fibres, is from the nature of ite 

 origin a complex structure. Its texture is not 

 always the same; it may l>e covered with minute 

 adhesive beads, or be stronger and nnbcaded, or 

 very liulit and filmy as in gossamer. In some 

 spiders there is a special chitinous plate called 

 the cribellum lying in front of the spinnerets and 

 perforated by the ducts of numerous glands. ' Its 

 presence is correlated with that of the calamistrum, 

 a single or double row of long wavy hairs on the 

 dorsal aspect of the second last tarsal joint of the 

 fourth pair of walking-legs. One of the calamistra 

 is rapidly vibrated over the criltellum, ami draws 

 out the secretion from the glands in the form of 

 threads, used to strengthen the web, to assist in 

 forming the cocoon for the eggs, and sometimes 

 perhaps in making a domicile.' 



The webs of spiders vary as much as do the 

 nests of birds, but as a single example of their 

 making we may take that of the Common Harden 

 Orb -weaver 

 ( Epeira dia- 

 tli'iiin ). The 

 spinner first lays 

 down a number 

 of linn founda- 

 tion-lines, which 

 may be disposed 

 ' by hand ' if the 

 situation admits 

 of this, but are 

 more frequently 

 blown fortuit- 

 ously by air-cur- 

 rents. Having 

 secured a num- 

 ber of these 

 foundation-lines 

 enclosing the 

 area for the 

 web, the spider 

 forms the radii 

 which intersect 

 in the centre. 



Fig. S. Garden Spider spinning her 



wrl.. 



( From ' Rlvenlde ' Natural H<*ory.) 



This done, she begins from the 

 centre and stepping outwards in a wide spiral lays- 

 down the spiral scaffolding. Finally, beginning at 

 the circumference and working inwards, the spider 

 lays down the delicate viscid spiral- on which the 

 efficiency of the web depends. The primary spirals 

 simply form a scaffolding, and are undone, in fact 

 eaten up, as they are replaced. But the web of the 

 garden spider is a comparatively simple case ; we 

 nave to distinguish 'orb-web-.' ril.Umed orlis," 

 'composite snares and sectional orb-.' 'hori/ontal 

 snares and domed orbs,' ' unloaded oral and spring 

 snares,' and so on, as Hi McCook, in his incompar- 

 able work on American spiders, has pointed out 



