FORMATION OF ANIMAL AGGREGATIONS 49 



Hyponomeuta, which inhabit an irregularly rounded web usually 

 placed between several branches of the food plant. The individual 

 larvae exhibit no tropisms except a strong negative stereotropism. 

 When placed singly on the ground, the larvae make a looplike path. 

 They stop at almost every point of the loop and test out their en- 

 vironment with their heads, selecting thus a place to lay their silk 

 thread. Single caterpillars spinning their web behave similarly. The 

 individual reaches out as far as possible from the place of beginning 

 and lays down its thread. This action is repeated and results in a 

 spreading of the web. Such a response to space Szymanski regards 

 as a negative stereotropism. 



In one experiment eight caterpillars were observed in nest-build- 

 ing. Six were placed together at one place, and one each at two 

 slightly distant points. All began spinning webs as described above. 

 The six spun a common web, which finally reached and fused with 

 the webs of the isolated caterpillars, so that a joint web resulted. 

 This probably happens in nature. So far, there are no reactions re- 

 maining over and above the individual responses, and Szymanski 

 concludes that in the formation of this common web there are no 

 secondary or purely social reactions. 



Deegener (1922) disagrees with Szymanski 's observations and 

 with his interpretations, particularly the latter. He, too, found that 

 isolated Hyponomeuta larvae can spin webs, but concluded that they 

 do not begin spinning as soon as if grouped together, and that the 

 web spun by a group is smaller than that made by the union of webs 

 spun by the same number of isolated larvae. In both respects he 

 would recognize the working-out of a social instinct. Further, he 

 believes that the caterpillars actively seek out the company of 

 others, guided by sensing vibration waves, which may be merely 

 refined touch perception. Back of all this he believes there is a need 

 for association which leads the isolated larvae to seek their own kind. 

 If they do not find their fellows, they build their own individual 

 nests, which later they may abandon, wandering and seeking in 

 order to associate themselves with other larvae. If none are found, 

 they may remain solitary for days without losing their social in- 

 stinct. 



