56 LIFE : OUTLINES OF GENERAL BIOLOGY 



like. Fabre tells how a family of spiderlings hatched out at the 

 foot of a high pole proceeded to climb up and up, day after day, till 

 they reached a very absurd height. No doubt the young spiders are 

 experiencing an autumnal restlessness, but we may be sure that 

 they do not climb up to a vantage-point because they argue that 

 they will thus get a better send-off. They are obeying what is, 

 nowadays at least, a racially enrcgistered tropism to climb against 

 gravity. 



The spiders dispose themselves with their head towards the slight 

 breeze, and it is interesting that the thread-spinning instinct will 

 not become active unless there is a current in the air. Blackwall 

 showed long ago that spiders imprisoned on a flower- pot in a room 

 would not begin to parachute until a slight draught was produced 

 by opening a window. Some air-current is needed as the instinct- 

 liberating stimulus. 



The spider pays out a thread of silk, or there may be as many as 

 frmr. In any case, though we say "as thin as gossamer", each thread 

 is a multiple jet of liquid silk, hardening instantaneously on exposure 

 to air. When the wind begins to tug, the spider lets go with all its 

 eight legs at once and, usually turning upside down at the same 

 moment, is borne on the wings of the wind to an unknown goal. 

 Careful observers assure us that it can add to the length of the 

 ballooning threads if the wind falls; and it can furl its sail if the 

 wind rises. Sooner or later it begins to coil in the threads, and thus 

 it sinks to earth, perhaps many miles from the starting-place. 

 When tens of thousands of spiders do this on a fine autumn day, 

 there may be an extraordinary shower of gossamer covering acres 

 of links and lea. Many of the threads we see floating in the air have 

 no spider attached; these may be broken off failures or they may be 

 threads that have served their purpose. 



It takes an appreciable time to write the words climbing, posing, 

 spinning, vaulting, parachuting, but the process often takes place 

 with great rapidity. Almost before we could say "go.ssamer" we 

 have seen a small spider run along our finger and set sail from the 

 tip. It is an instinctive perforitiance, requiring no individual appren- 

 ticeship. Two other notes may be useful. First, there is no particular 

 kind of gossamer-spider, for the habit is exhibited by many young 

 small spiders belonging to light-loving species. Secondly, gossamer 

 is by no means restricted to autumn, its conspicuou.sncss at that 

 time of year lx»ing due to the fact that spiderlings are then most 

 numerous and most crowded. 



For there is no doubt that the ballooning is a method of passive 

 disjxTsal, which enables the spiders to get away from places that 

 are overcrowded or overdr\% or very scantily frequented by the 

 insects on which spiders depend for food. There is no doubt that this 

 neat device of flying without wings sometimes spells disaster, for 



