198 ARACHNIDA. 



taking a few steps, stop suddenly, and rear themselves on 

 their fore-legs. Should they see a fly or gnat, they 

 approach it cautiously, until they get so near that they 

 can clear the distance at a single leap, and then spring 

 like tigers on their prey. They may often be seen to 

 make these leaps even from a perpendicular wall, for 

 being always attached by a silken thread, they easily 

 scramble up again. Many of them build their nests 

 under stones, or between the leaves of trees. Their nests 

 are of an oval form, and open at both ends : in these they 

 repose, change their skin, or take shelter from the 

 weather ; but if alarmed, they immediately rush out, and 

 scamper off with precipitation. 



Some spiders possess the remarkable faculty of shoot- 

 ing out threads in diverging lines into the air, which, 

 being lighter than the atmosphere, form a sort of balloon, 

 on which the little aeronaut mounts above this lower 

 world, and rides at will among the clouds. 



Mr. Blackwall supposes that the spider is enabled to do 

 this by the action of the wind, which carries the thread 

 out as it is spun, and that many being entangled together, 

 are carried into the air by the upward current, caused by 

 the rarefaction of the stratum near the heated ground, 

 during the middle of the day ; and that at night, the earth 

 being cooled, the air descends, bringing with it the accu- 

 mulated webs, which, lying thick upon the herbage, are 

 called gossamer. 



Mr. Darwin's observations relative to these gossamer 

 spiders are very interesting. His ship was sixty miles 

 from land, in the direction of a steady though light breeze, 

 and vast numbers of small spiders covered the rigging 

 with their webs. 



" The little spider, when first coming in contact with 

 the rigging, was always seated on a single thread. The 

 little aeronaut, as soon as it arrived on board, was very 

 active, sometimes letting itself fall and then reascending 

 the same thread, sometimes employing itself in making a 

 small and very irregular mesh in the corners between the 

 ropes. While watching some that were suspended by a 

 single thread, the slightest breath of air bore them out of 

 sight. I repeatedly observed the same kind of small 

 spider, either when placed or having crawled on some 

 little eminence, elevate its abdomen, send forth a thread, 

 and then sail away in a lateral course, with a rapidity 



