15 



Notes on Argyroneta aquatica and some other Spiders. 



By Rev. F. H. Wood, M.A. Read April 2'$,th, 1904. 



Among what writers of little handbooks on aquaria used to call 

 " interesting objects," few perhaps can compete in attractiveness 

 and pleasing qualities with Argyroneta aquatica, known as the 

 diving water spider. 



It is, however, a question, whether in most cases this Arachnid 

 has not been kept and observed more for its appearance and inter- 

 esting habits than for purposes of scientific study. Still, there must 

 have been a strange lack of observation if a desire for more know- 

 ledge as to the habits of this and other spiders has not been, in 

 some way, kindled. And, further still, the whole question of sub- 

 aqueous respiration is brought into prominence by the silvery gleam 

 of the sheath of air, enclosing the whole of the abdomen, and 

 extending along the sternum, or breastplate, under the cephalo- 

 thorax. 



The same fundamental scientific axiom, that organisms breathing 

 atmospheric air must be in possession of a sufficient supply if life is 

 to be maintained under water, has been, perhaps, already noticed 

 in evidence in the case of aquatic Coleoptera : for instance, in such 

 arrangements as the anal bubble retained by the Dytiscidce and 

 Gyrinidse, closing and revealing the supply of air lying over the 

 spiracles under the elytra ; and the film of air lining the whole 

 under-surface of the Hydrophilidfe, accomplishing the same life- 

 sustaining work in a different way, as again in the case of Hemiptera 

 like Notonecta glaiica. 



There is, however, one broad, universal method in the retention 

 of external air, made use of alike by spider, beetle, or bug, namely, 

 its entanglement on a hairy, or downy, and somewhat oily surface. 

 This will be found to be the case whether we examine the hairy 

 fringe slightly visible on the upper surface of the abdomen, beyond 

 the elytra, of Dytiscus marginalis or Gyrinus natator, or the strongly 

 marked pubescence of (say) Hydrous piceus and Notonecta glauca. 

 But, in the case of spiders, this adaptation is most conspicuous, 

 not only in A. aquatica, but in members of the family Lycosidse, 

 of the Genera Dolomedes and Firata, to which I hope to refer 

 further on. 



The abdomen of A. aquatica is very hairy, the hairs on the under 

 surface are of considerable length, as well as those which are thickly 

 set on the sternum. Sufficient air is thus retained to cover and 

 supply the breathing-holes on the lower side, near the base of the 

 abdomen, and also to prevent its soft 'covering from becoming 



