Culex territans Walker (Diptera: Culicidae) larvae share nonpolluted freshwater habitats with amphibians, which are bloodmeal hosts of their adults. To examine synchrony of Cx. territans with amphibian species, 10 larval habitat sites were sampled weekly from March to November of 2004. Cx. territans larvae were temporally and spatially associated with the green frog, Rana clamitans Latrielle. We predicted that if the preferred hosts were abundant at low temperatures, Cx. territans might be able to digest bloodmeals at those same temperatures. Using the thermal heat summation model, 192.3 d above 3.9 degrees C were needed to complete the gonotrophic cycle. This is the lowest thermal minimum reported for a Nearctic species of mosquito. Using this model, we calculated that the first larvae of Cx. territans field collected on 6 May 2004 were the progeny of females that bloodfed during the last week of March or first week of April. We conclude that Cx. territans has physiological mechanisms that allow them to take advantage of early season bloodmeal sources.