62 



NA TURE 



[November i6, 189; 



her back. This circumstance, coupled with the fact that 

 iio specimen of this spider ever gave the smallest sign 

 'jf knowing the direction whence the sound proceeded 

 anless its web was actually touched with the tuning-fork, 

 is in favour of Dr. McCook's view, that the EpeiridcE, 

 which respond readily to a tuning-fork that is held near 

 them, are only aware of the proximity of the vibrating 

 instrument through the responsive vibration of the web. 

 This may be the true explanation with regard to Amaii- 

 rol'u/s, but there are several reasons, as will shortly be 

 seen, which lead me to think it is not so where the 

 Epeiridce are concerned. 



Pholcus phalangioides, belonging to a group by itself, 

 is a common spider in many parts of the south of England. 

 It frequents kitchens and outhouses, where it spins a very 

 untidy-looking web, composed of irregularly interlacing 

 loosely-woven threads. The species cannot be readily 

 mistaken for any other true British spider, on account of 

 the extreme length and thinness of its legs. Owing to 

 this peculiarity, it is probably largely responsible for the 

 popular but erroneous idea that the Opiliones — the 

 harvest-men or long-legged spiders pm- excellence — can 

 spin webs. Whenever any part of the web of a Fholeiis 

 was touched with a vibrating tuning-fork, the occupant 

 would come clumsily and leisurely up to the instrument, 

 and when it was held close to the back of the spider, the 

 latter would show its perception of the vibration by slowly 

 lifting its legs. One specimen away from its web re- 

 sponded in exactly the same manner as the others did 

 when hanging in the midst of their snares, thus showing 

 that it is not the vibration of the web that informs this 

 species of the proximity of the instrument. 



Epeira diadeinata^ Met a segiucntata, andZt7/a x-7iotata, 

 are three very common spiders belonging to the group of 

 Orb-weavers. The first-named — the common garden or 

 cross-spider of England, one of the largest of our species 

 — is known to every one. Meta segnieniata, too, is very 

 abundant, spinning its web in hedges and bushes ; it may 

 be easily recognised from E. diadciitata by its much 

 smaller size and more graceful build. Zilla is more like 

 Mcta than Epeira, being a smallish, rather graceful 

 species, which spins its web very commonly in the angles 

 of windows, &'c. The structure of its web also affords 

 another clue to its identity, for while in Epeira and Mcta 

 the snare is a complete orb, the concentric lines extend- 

 ing across all the radii from the centre to the circum- 

 ference, in Zilla, as a very general rule, two of the inter- 

 radial spaces in the upper half of the web are not crossed 

 by the concentrices : the circle of the web thus lacks one 

 sector, and the resulting triangular space is traversed by 

 a free radius, which is continued beyond the circum- 

 ference of the snare, and connects its centre with a second 

 small irregular web, which is spun in a crevice or beneath 

 some leaf. 



Like most other spiders these three species will usually 

 come to a vibrating tuning-fork, if the web be touched 

 with it. And if it be held over the centre of the web 

 where the spider is hanging, the three will readily respond 

 to the sound ; but not in the same way. As Mr. and 

 Mrs. Peckham and Prof, Boys* have shown, an adult 

 Epei7-a diadei/iata raises its forelegs and snatches at the 

 instrument, while Meta - scgmentata instantly drops by a 

 thread from her snare ; but Zilla, so far as my experience 

 goes, instead of dropping like J/tV;?, nearly always climbs 

 quickly along the free radius back to the upper web. 

 One example, however, repeatedly dropped from its web, 

 and two others, one adult and one young, moved excitedly 

 about as if in search of the cause of the sound, exactly 

 as described in the case of Amatirobitis. Curiously 

 enough the sound affects the examples of diadcmata dif- 

 ferently according to their age. Thus quite small examples 



1 Nature, vol. xUii. pp. 40-41. 



' This is probably the small unidentified orbicular spider that Prof. Boys 

 speaks of. 



NO. 1255, VOL. 49] 



drop by a thread, but half-grown examples either drop as 

 the young do, or strike at the fork like the adults. It 

 appears therefore from these facts, that as a general rule 

 the small English Epeirid^e fear the sound of a vibrating 

 tuning-fork, while the large ones do not. What is the 

 explanation of this '^. Prof. Boys, who has previously 

 noticed thissame fact in connection with E. diade/nataand 

 Meta, thinks that it is perhaps to be explained on the 

 grounds that the vibrating tuning-fork is mistaken for an 

 approaching wasp — aninsect which, to use Dr. McCook's 

 words, " is the most persistent enemy of spiders." But 

 a full-grown E. diademata is too formidable an opponent 

 for a wasp to attack, and it seems well aware that any- 

 thing buzzing can be overcome and eaten, or at least 

 repulsed. Not so, however, is it with a Meta. A wasp 

 can take one of these small spiders out of its snare while 

 still on the wing, and the spider's life depends upon the 

 quickness with which it can perceive the approach of its 

 enemy and act upon the perception by dropping out of 

 harm's way. 



This ingenious suggestion is further borne out by the 

 behaviour of Zilla and of the young diadematas, for these 

 spiders would have no more chance against a wasp than 

 Meta has. Moreover, my friend Mr. Henderson, of 

 Madras, has informed me that he has repeatedly seen 

 examples of a common Indian house spider* drop from 

 their webs at the approach of the mason-wasps. 



Such a habit, then, of falling or running away would 

 clearly give a spider that possessed it an advantage in 

 life over others of the species in which if^was not de- 

 veloped, and the elimination of the latter an'»d the survival 

 of the former, with the consequent chance of breeding, 

 would foster the habit and bring it to the state of perfec- 

 tion in which we now see it. 



On the other hand, the loss of the habit in the adult iT. 

 diademata, may perhaps be explained on the hypothesis 

 that the act of dropping entails the expenditure of energy 

 in the form of waste of silk and of muscular tissue ; more- 

 over, it might at the same time on occasions lead to the 

 escape of an insect that would have served for prey if the 

 spider had remained in statu qi(o. The two instincts 

 are seen in a state of transition in haXi-grown diadeviatas. 

 But the acquired one of fearlessly fighting the enemy 

 would be prevented from appearing too early in life by 

 the destruction of those individuals which, with over- 

 confidence on their growing powers, stayed in the web 

 when they ought to have dropped from it ; or, in other 

 words, the runaway instinct would be preserved as long 

 as the spider was too small to cope with a wasp. 



Another interesting question connected with this 

 behaviour of the Epeiridce is the means whereby the 

 vibration of the fork is perceived. The obvious answer 

 is that the sound is heard. But Dr. McCook has re- 

 cently objected to this explanation on the grounds that 

 the Lycosida?, which spin no web, and which, in Dr. 

 McCook's opinion, have more need of an auditory sense 

 than the Epeiridte, make no response when the vibration 

 is brought near them. 



It has been objected {Ann. Mag. Nat. Hist. Ser. 6, viii. 

 p. 103), however, to this opinion of McCook's that the 

 Epeirida; which spin their webs in places where flies are 

 likely to be caught, must of necessity at the same time ex- 

 pose themselves to the attacks of wasps. We can therefore 

 imagine that it is of the highest importance to them to 

 be able to perceive the approach of their enemy — of more 

 importance to them, in fact, than to those spiders, which 

 like the Lycosidae spin no exposed and conspicuous snare, 

 and are therefore more likely to escape the notice of 

 the wasps. 



To account for- the behaviour of the Epeirids when a 

 vibrating fork is brought near them. Dr. McCook has 

 suggested that the vibration of the instrument causes 



1 Mr. Henderson i<indly procured examples of this spider for me, and they 

 proved to belong to the genus Fholcus. 



