The bamboo mosquito, Tripteroides bambusa (Yamada) (Diptera: Culicidae), is a common insect across forested landscapes in Japan. Several studies have reported its overwintering as larvae and eggs, in both natural and artificial water containers. Nevertheless, it is unclear how sensitive this mosquito species is to changes in weather patterns associated with global warming. The El Niño event of 2015 through 2016 was one of the strongest on record and provided an ideal scenario for observations on the overwintering of the bamboo mosquito during a winter predicted to be unusually warm. Thus, we set oviposition traps in mid October 2015 and made weekly observations, from December 2015 to May 2016, on bamboo mosquito larval recruitment and pupation in Nagasaki, Japan. We found that larvae were pupating as late as the first week of January (prior records from the study site indicated mosquito pupation ended by mid-late October) and that pupation resumed in mid April (one month earlier than previous records at the study site). We also found that fourth instar larvae were able to survive in frozen oviposition traps following an extremely unusual snowstorm and cold spell and that recruitment of larvae from eggs happened after this unusual event. Our analysis suggested that overwintering and metamorphosis of the bamboo mosquito is sensitive to average and extreme temperatures, the latter measured by temperature kurtosis. Our results highlight the need to better understand changes in overwintering strategies in insects, and associated trade-offs and impacts on population dynamics, in light of climate change.