i8 ANIMAL AGGREGATIONS 



a) Sympaedium, in which the offspring of the same mother form 

 the aggregation without the presence of either parent. This concU- 

 tion is seen in some spiders and insects, where the young of the same 

 mother remain together for a longer or shorter period. If the mother 

 remains with the offspring, the group belongs to another category. 

 Lophyrus caterpillars, which feed on pine needles, form an aggrega- 

 tion due in the first place to the eggs being laid together. No obvious 

 benefit accrues to the individuals. They are more conspicuous as a 

 result of the grouping and cannot defend themselves better than if 

 alone. The causal factors in such an aggregation are obscure. The 

 fact that the eggs are laid together is not sufficient in itself, since 

 other forms have their eggs laid similarly close together and yet 

 separate immediately on hatching. It may be that the sluggishness 

 of the animals and the lack of disrupting stimuli explain a large part 

 of the behavior; while, on the other hand, there may be a social 

 appetite which holds the groups together. The problem becomes 

 more difficult with those larvae which remain together during the 

 early larval hfe and separate when partly grown. 



Many lepidopterous larvae that remain together during part 

 or all of their larval life spin a common nest. The formation of 

 such a nest may be due to the fact of living together rather than the 

 living together being due to the need or use of a common nest. The 

 abihty to spin a common nest does not guarantee the actual building 

 of one, for many spinning animals live alone. These larval colonies 

 are common among animals in which the adults are winged, and 

 hence are readily distributed during that phase of their life-history. 

 Such a sympaedium occurs in sohtary bees which lay eggs in cells. 

 The resulting larvae and pupae form an accidental association, living 

 together as offspring of a common mother. When adult, they fly 

 away separately. 



h) A gynopaediiim is composed of a mother and her offspring that 

 remain together for a period. This grouping is not concerned with 

 the relationship between mother and offspring beyond the fact that 

 they remain together without obvious benefits accruing to the group 

 from the association. The aphid stem-mother in the spring gives 



