290 



ANIMAL MOVEMENl 



winged fly, which, though unprovided with any special expansions 

 of the body, is carried passively along by the wind, being remi- 

 niscent in this respect of certain small marine animals that drift 

 along in the surface currents of the sea. The fly in question 

 (^Hirmoneura obscura) deposits her eggs in the tunnels which 

 have been excavated in logs by wood-boring insects. When 

 the maggots hatch out they make their way to the outside of 

 the log, and sit up on their tails till they are blown away by the 

 wind. When next met with they are found preying upon certain 

 beetle-grubs which live in turf but whether they attain their goal 

 by pure chance is not known. 



Many Spiders and some few Insects spin threads which 

 present a sufficient surface to the wind to enable them to act as 



kites, bearing their constructors 

 through the air, or at any rate ren- 

 dering aerial progress more easy. 



Spiders (Araneid.«) as Kite- 

 Flyers. — The floating spider - 

 threads familiar to all as " g'os- 



o 



samer " were once believed to be 

 produced by one particular kind of 

 spider, but it is now known that 

 they are spun by young individuals 

 of many species. They are par- 

 ticularly abundant in early autumn, at the time associated with 

 the slaughter of Michaelmas geese, and as the word is sup- 

 posed to be a corruption of "goose-summer", it was possibly 

 originally given on this account. A young spider desirous of 

 floating through the air by this means stands firmly on its first 

 three pairs of legs (fig. 828), and begins the work of spinning, 

 using the last pair of legs for manipulating the threads. One 

 of these is an anchor-line, and is severed when the eossamer 



o 



thread is sufficiently long to serve its purpose. Krieghoff gives 

 the following account of the matter (in Das Tiem^eicli): — "Webs 

 not only enable spiders to secure their prey, but also serve as 

 a means of locomotion. In autumn young spiders begin to dis- 

 perse themselves, casting out in any desired direction threads of 

 such wondrous fineness as only to be visible in sunlight. By cling- 

 ing to these with legs drawn in, these daring aeronauts are able 

 to traverse considerable distances. The object of this procedure 



Fig. 828. — Young Spider spinning a "Gos- 

 samer" Thread. The arrow shows the direction 

 of the wind 



