ORB-WEBS 349 



venomous jaws of its captor. Sometimes the insect is so power- 

 ful, or the spider so sated with food, that the latter hastens to 

 set free the intruder by biting away the threads which entangle 

 it before much havoc has been wrought with the net. 



The viscid matter on the spiral line dries up after some 

 hours, so that, even if the web has not been destroyed by insects 

 and stress of weather, this portion of it must be frequently 

 renewed. Commencing a new web is, as has been seen, a 

 troublesome matter, and it will readily be understood that the 

 spider prefers, where practicable, to patch up the old one. This 

 is done by biting away torn and ragged portions and inserting 

 new lines in their place. 



The part played by the various spinning glands in the con- 

 struction of the orb-web may be briefly stated.^ The ampullaceal 

 glands furnish the silk for the foundation lines and radii. The 

 spiral has a double ground -line proceeding from the middle 

 spinnerets, but it is not quite certain whether it proceeds from 

 the ampullaceal or the tubuliform glands. The chief function of 

 the latter, in the female, is to furnish silk for the egg-cocoon. 

 The viscid globules are the products of the aggregate glands. 

 The aciniform and piriform glands provide the multitudinous 

 threads by which the spider anchors its various lines and enwraps 

 its prey. 



Some Orb-weavers always decorate their snares with patches 

 or tufts of flossy silk. In the snare of the North American 

 Argiope cophinaria the hub is sheeted, and from it extends down- 

 wards a zigzajr ribbon of silk stretched between two consecutive 

 radii. A^inson ^ discovered a remarkable use for similar zigzag 

 bands in the web of the Mauritian spider, JEpeira mauritia. It 

 furnished a reserve supply of silk for enveloping partly entangled 

 insects whose struggles were too vigorous to succumb to the 

 rather feeble threads which the spider was able to emit at the 

 moment of capture. The spider was able to overcome a grass- 

 hopper much more powerful than itself by dexterously throwing 

 over it with one of its hind legs a portion of the ribbon of silk 

 which it had thus stored up for emergencies. 



Many orb -webs are defective, a sector of the circle being 

 uniformly omitted in the structure. The genus Hyptiotes does 



1 See Warburton, Quart. J. Mier. Sci. xxi., 1890, p. 29. 

 ^ AranHdes de la Riiunion, Maurice et Madagascar, Paris, 1863, p. 238. 



