INSTINCT OF INSECTS. 



387 



A remarkable instance of variation of instinct in the com- 

 mon house-spider (Aranea domestica) is mentioned by an 

 anonymous writer in the Zoological Journal. He states that 

 having placed one on a piece of wood fixed in the middle of a 

 glass of water, the spider, finding its other efforts to escape 

 ineffectual, enveloped its abdomen by means of its hinder legs 

 in a loose web which it spun, and then descended at once 

 without the least hesitation into the water, surrounded under 

 its mantle with a bubble of air, evidently intended for respir- 

 ation as it included the spiracles ; and in this extemporaneous 

 diving-bell, like that of the water-spider {Argyroneta aquatica) 

 before described, it endeavoured to make its escape on every 

 side, but, on account of the slipperiness of the glass, in vain ; 

 and after remaining at the bottom of the water for thirteen 

 minutes, it returned apparently much exhausted, as it coiled 

 itself under its wooden platform without motion. 1 As we 

 cannot refer so philosophical a contrivance to reason, we must 

 regard it as a variation of instinct ; but certainly, if correctly 

 reported, a very curious one, as the occasions on which the 

 house-spider can want to escape through water must be very rare. 



In the preceding instances the variation of instinct takes 

 place in the same individual ; but Bonnet mentions a very 

 curious fact, in which it occurs in different generations of the 

 same species. There are annually, he informs us, two gener- 

 ations of the Angoumois moth, an insect which has been before 

 mentioned as destructive to wheat : the first appear in May and 

 June, and lay their eggs upon the ears of wheat in the fields ; 

 the second appear at the end of the summer or in autumn, and 

 these lay their eggs upon wheat in the granaries. These last 

 pass the winter in the state of larvas, from which proceeds the 

 first generation of moths. But what is extremely singular as 

 a variation of instinct, those moths which are disclosed in May 

 and June in the granaries quit them with a rapid flight at 

 sunset, and betake themselves to the yet unreaped fields, 

 where they lay their eggs ; while the moths which are dis- 

 closed in the granaries after harvest stay there, and never 

 attempt to go out, but lay their eggs upon the stored wheat.* 2 



1 ZoohgicalJourn. i. 284. 



c c 2 



2 CEuvres, ix. 370. 



