Group foraging is rare in spiders, occurring only where prey availabil
ity is high. If colonial web-building increases individual prey captur
e rates as shown, why does group foraging not occur more often where p
rey are scarce? Risk sensitivity may explain this paradox, as variance
in prey capture is reduced in groups; risk-averse spiders should join
groups only when prey exceed a threshold level. Field studies show th
at group foraging varies as predicted between species, between populat
ions of a single species, and between sites within a population. Howev
er, recent models suggest the necessity of examining variance within i
ndividuals over time rather than between individuals within population
s. Additionally, mechanisms responsible for variance reduction in colo
nial webs may be less effective than previously assumed. New field dat
a suggest that while prey variance over time may be somewhat less for
individual spiders in groups than for solitaries, the relationship bet
ween colonial web-building and variance in prey capture is far more co
mplex than originally thought. The influence of risk sensitivity on re
productive success and the evolution of colonial web-building is discu
ssed.