Eggs of field crickets (Gryllus spp.) held at 25±1°C hatch in 2-4 weeks ("fast-developing" eggs) or 5-28 weeks (diapause eggs). Most species lay but one type: at least 10 species lay only fast-developing eggs, and pennsylvanicus and ovisopis lay only diapause eggs. Gryllus firmus from Gainesville, Florida, lays both types, and individual females do so for as long as 8 weeks. The proportion of diapause eggs laid weekly by captive females exposed to outdoor photoperiods and temperatures varies seasonally from <5% (March-June) to ca. 50% (November-December). At outdoor temperatures in late fall some eggs that are presumptively fast-developing (at 25° C) enter diapause.Some firmus from Carolina Beach, North Carolina, lay both diapause and fast-developing eggs. Outdoor rearing experiments established that spring adults could result from fast-developing eggs of fall adults, refuting the hypothesis that spring and fall adults at that locality represent temporally isolated demes.High variance in hatching times for eggs laid by one female is appropriate to the unpredictable extremes of moisture and temperature that occur in the open, sandy habitats of G. firmus. Physiological mechanisms of the mixed oviposition and specific environmental determinants of the varying proportions are unknown.