160 



AMERICAN SPIDERS AND THEIR SPINNINGWORK. 



ning over water, and behavior when cast upon water, I wished to observe. 

 Tlie beaten marsh grass yielded me no Dolomedes, but instead several 

 liaK grown Tetragnatha vermiformis, Emerton, dropped upon the surface. 

 To my surprise they seemed not the least disconcerted, but immediately 

 recovered themselves and with one exception ran to the shore precisely 

 as do the Lycosids. The excepted individual had been thrown out from 

 the bank farther than its comrades. For a moment it paused, its body 

 bowed and held upward upon the eight legs which were spread out so 

 that the feet marked the outline of a rude circle upon the surface. Then 

 it started rapidly across the mouth of a tiny baylet between a tongue of 

 the land and the main shore, traversed the intervening space, 

 \ \ and pulled itself to the land by the overhanging grass. My 



attention was attracted by the remarkable fact that during 

 this transit there was no appreciable movement of 

 the legs. That an Orbweaver should be able to glide 

 so rapidly and gracefully over water was a fact 

 in itself sufficiently now to me ; but that one 

 should do this without any physical exertion 

 whatever amazed me. Could the action of the 

 air upon the body have been the impelling force ? 

 I addressed myself eagerly to the solution 

 of this mystery. A second clump of grasses 

 was beaten, and a Tetragnatha fell upon the 

 lake. She ran over the water to tlie shore, 

 using apparently her fore legs as paddles. Be- 

 fore she climbed into the grasses I 

 thrust my cane under her body, 

 gently lifted her up, and reaching 

 outward as far as I could, gradually 

 sunk the tip of the stick into the 

 water without causing any ruffling 

 of the surface. The spider was thus 

 eased oif the stick and placed upon 

 the surface undisturbed. As soon as she felt herself fairly launched she 

 made a few strokes with her fore feet, then suddenly paused and thrust the 

 apex of her abdomen down to the surface. Directly, the abdomen was 

 raised from the water and turned up until it made an angle of about 60° 

 with the surface. Next a long streamer of silk filaments was emitted from 

 the spinnerets, precisely as in the case of aeronautic spiders when about to 

 ascend, and immediately the spider began to scud at a great rate over the 

 water. The mysterious motor was thus revealed — the silken threads served as 

 sails upon which the wind played, propelling the vital craft across the water. 

 The discovery into whicli I was thus accidentally led was so interesting 

 that I devoted the remainder of my day to the full investigation of the habit 



Fig. 152. Silken sails : Tetragnatha navigating a lake. 



