274 



NATURE 



[July 21, 1898 



labour as no other institution could be found ready to 

 take up." That policy has been steadily pursued 

 throughout this, its first, half-century of existence, and by 

 the perusal of this volume most readers will be convmced 

 that it has been justified by the results. H. R. 



SPIDER AND PITCHER-PLANT. 



IN the insectivorous plants of the genus Nepenthes, a 

 form represented by a number of species and widely 

 •distributed over the Indian and Australian regions, as 

 well as in Madagascar, the pitchers or insect-traps, which 

 are usually regarded as expansions of the leaf-stalk, are 

 suspended, mouth upwards, at the ends of long tendrils 

 proceeding from the tips of the leaves. The gaping 

 orifice, frequently strengthened and kept open by a 

 thickening of the rim, is protected by a lid, which, while 

 preventing the infall of rain, offers no obstruction to the 

 free entrance of insects. To attract the attention of 

 these animals the pitchers are frequently conspicuously 

 coloured in their upper parts, and honey is secreted from 

 glands scattered around the margin of the aperture and 

 on the under-face of the lid. This gaudy and sweetened 

 portion, designed as it is to catch the eye and act as a 

 bait, constitutes the " attractive " area. A short distance 

 within the cavity and below the attractive area just de- 

 scribed, the walls of the pitcher are smooth and of a 

 waxy consistency, so that no foothold is afforded to in- 

 sects, which are consequently precipitated to the bottom 

 ■of the pitfall if luckless or incautious enough to venture 

 on this " conductive " area. The lower part of the re- 

 ceptacle is filled to a greater or less extent with a fluid 

 ■containing, amongst other substances, potassium chloride, 

 malic and citric acids, as well as soda lime and magnesia 

 in smaller quantities and an enzyme, which in the presence 

 of the acids has the power of digesting organic matter 

 (S. H. Vines ; quoted by "A. W. B ," Nature, vol. Ivii. 

 pp. 367-368, 1898). This fluid, poured out as a secretion 

 from a large number of glands developed in the adjacent 

 walls of the pitcher, is usually crowded with the in- 

 digestible remains of insects, commingled with those of 

 which the nutritious tissues are in process of decom- 

 position under the action of the alimentary juice of the 

 plants and of the bacteria which infest it. 



The spiders of the family Thomisidas belong to that 

 artificial section of the order sometimes spoken of com- 

 prehensively as the wandering or hunting species as 

 opposed to those of sedentary habit, which spin snares 

 for the capture of prey. Some of the Thomisidas live 

 on the ground amongst vegetable debris or beneath 

 stones ; others on the trunks or leaves of trees ; others, 

 again— and these are the species that have attracted the 

 greatest amount of attention — frequent flowers, and lurk 

 amongst the petals on the watch for visiting insects. To 

 this last category belongs the spider {Misumena nepen- 

 thicold) now under discussion, a species which invariably 

 takes up its abode in the pitcher of a North Bornean 

 (Labuan) Nepenthes, perhaps referable to the species 

 described as N. phyllamphora} In any case, whatever 

 the name of the plant may be, the Misumena appears to 

 inhabit exclusively the one species ; for although several 

 other kinds were found growing in the vicinity, they were 

 never observed to be tenanted by spiders. 



According to that skilled collector and trustworthy 

 observer, Mr. A. Everett, who kindly furnished me with 

 the notes forming the basis of the account here given, 

 the pitchers in question are somewhat elongate in shape, 

 and constricted a short distance below the rim, broadening 

 out again as the bottom is approached, and narrowing 

 ultimately to a vanishing point where they join the sup- 



1 I am indebted to my colleague, Mr, A. B. Rendle, for kindly examin- 

 ing the two fragments of the pitcher sent home with the spiders. Unfor- 

 tunately the pieces are too small to make the identification of the species 

 •other than doubtful. 



NO. 1499, VOL. 58] 



porting stalk. Just below the upper constriction the 

 spider spins a slight web, adherent to the wall of the 

 pitcher. This web is not of the nature of a snare or net 

 designed to intercept insects, but extends as a thin carpet 

 over a small portion of the conductive area, and enables 

 the spider to maintain a secure hold on its slippery sur- 

 face. Here it lives and rears its young, no doubt feeding 

 upon the insects which the Nepenthes attracts for its own 

 use, capturing them either as they enter the pitcher, or 

 perhaps after they have fallen into the digestive fluid 

 below. 



So far as procuring food is concerned, this spider would 

 seem to be no better off than those of its allies which 

 live in flowers and capture the honey-seeking insects that 

 visit them, except in so far as it is not dependent upon 

 seasonal inflorescence for a place wherein to lurk. But 

 in one very important respect it must presumably score 

 heavily in the struggle for existence — that is to say, in 

 its means of escaping from enemies. 



It is a well-known fact that almost all spiders, especi- 

 ally those that occur in tropical and subtropical coun- 

 tries, suffer immense mortality from the relentless perse- 

 cution of the solitary mason wasps, which at their breeding 

 season scour the country and explore every nook and 

 cranny in the eager search for spiders wherewith to lay 

 up a sufficient store of food for the voracious young 

 wasps during the days of their larval existence. From 

 these enemies the flower-frequenting species have no 

 means of escape, except such as is afforded by quiescence 

 in conjunction with the protective nature of their colours, 

 attitudes and form. The slightest movement on their 

 part will attract the notice of the quick-sighted wasp, 

 and bring swift destruction upon them. 



Whether or not the mason wasps have the temerity to 

 invade the pitchers of Nepe7tthes in their quest for 

 victims, there is no evidence to show. Possibly long- 

 billed birds thrust their beaks into the insect-trap to 

 extract any living things or organic debris they may con- 

 tain. At any rate, the account given by Mr. Everett of 

 the behaviour of this spider when threatened with danger, 

 points forcibly to the conclusion that the species is sub- 

 ject to persecution from enemies of some kind or other. 

 This collector found that when an attempt was made to 

 capture them by tearing open the pitcher, the spiders, 

 although very active, never attempted to escape from the 

 mouth of the vessel, but ran down its inner surface, and 

 plunged boldly into the liquid at the bottom, ultimately, 

 if still pursued, retreating to its very base, and burying 

 themselves amongst the remains of ants, moths, beetles, 

 &c , with which the pitcher was more or less choked. 



Although many spiders of semi-aquatic habits, such as 

 Dolomedes, Thalassius, and some species of Lycosidce 

 plunge beneath the surface of water when threatened 

 with danger, and escape along the stems of the sub- 

 aqueous weeds ; and although an example of Araneus 

 {Epeira) cornutus, a terrestrial species which, however, 

 frequents the banks of streams and marshy country, has 

 been noticed, when disturbed, to drop to the ground, run 

 into the water, hide beneath a tuft of weed,i and there 

 remain for a minute or so before venturing to climb back 

 to its web, I am not aware that the adoption of water as 

 a city of refuge has ever been recorded of any member 

 of the family Thomisidte. These spiders, in fact, as already 

 explained, depend for safety upon protective assimilation 

 to their surroundings. Consequently the habit of plung- 

 ing into the fluid in the ^\\.ch&r oi Nepenthes, adopted by 

 Misumefta nepenthicola, must be regarded, it appears, as 

 a new instinct acquired by the species in connection with 

 the exceptional nature of its habitat ; and its behaviour 

 carries with it the conviction that the species is con- 

 stantly subject to persecution from some enemy other 

 than man, whether it be bird or wasp. 



Possibly the spiders, when once they have taken up 



1 Prof. Lloyd Morgan, Nature, vol. xlvii. p. 102, 1893. 



