An ovitrap with a time-segregated entrance was used to separate eggs laid by Aedes sierrensis females according to the time of day that females entered the ovitrap. During a 37-day period in Lake County, CA, females that entered the ovitrap between sunrise and sunset laid 82% of the total number of eggs collected. A daily peak in oviposition (eggs per hour) was produced by females that entered during the 2-h period ending at sunset. Overall, females that oviposited had entered the ovitrap throughout the diel cycle except for a 2-h period ending at sunrise. Those eggs laid by females that entered the ovitrap between 2 h after sunset and 2 h before sunrise provided the 1st evidence that Ae. sierrensis females are capable of locating oviposition sites during the night.