The behavioral evolution of the social Hymenoptera is often
viewed as a hypothetical continuum of species from solitary
to social (1), and studies of primitively social bees and wasps
have typically been interpreted in this context. However,
some recent investigations have emphasized intraspecific
variation in social behavior: single populations containing
individuals whose behavior ranges from solitary to eusocial
(2-5). Such behavioral diversity suggests that environmental
factors play a large role in the expression of social behavior
(C. D. Michener, personal communication). For many species, sociality may be facultative rather than obligate, permitting assessment of the immediate ecological pressures
favoring or inhibiting sociality. Such species may reveal some
of the ultimate origins of sociality and the behavioral mechanisms involved.