Several models for the economics of sociality demonstrate that the pro
bability distribution of an individual's resource consumption could de
pend on the size of its social group. When groups share food clumps di
scovered by any member, expected resource consumption may increase or
decline with group size, but the individual's resource consumption var
iance will ordinarily decline as group size increases. Hence, the form
ation and dissolution of social groups may represent risk-sensitive re
sponses to foraging success. A series of field studies report greater
mean prey consumption and decreased prey consumption variance as group
size in colonial spiders increases. Several hypotheses attempt to exp
lain this effect. Coloniality may promote acquisition of information c
oncerning temporal variation in prey availability. Colony membership m
ay permit individuals to steal food when the number of captured prey v
aries spatially. Finally, coloniality can enhance food acquisition bec
ause prey (that might otherwise escape) ricochet from one spider's web
to another group member's web. Our purpose was to quantify each hypot
hesis and ask if the resulting models predict reduced resource consump
tion variance as group size increases. We model each mechanism and con
clude that stealing prey is the simplest explanation for variance redu
ction in spider colonies. We emphasize that variance among individuals
need not provide a good estimate of the within-individual resource co
nsumption variance, and it is the latter variance to which risk sensit
ivity responds.