Egg hatch of blackheaded fireworm,Rhopobota naevana(H¨bner), was monitored in Wisconsin and British Columbia. In Wisconsin, hatch of overwintering eggs began during the last 2 wk of April, median hatch occurred during the first week of May, and hatch ended in late May. In British Columbia, hatch began in late March to early April, median hatch occurred in April, and hatch ended (except for one egg in both years that hatched in June) in late April in 1991 but extended into late May in 1992. Summer-generation eggs began hatching 2–7 d and completed hatch 6–15 d after oviposition in both regions. A linear spline model developed in Wisconsin predicted 50% hatch of overwintering eggs in Wisconsin to within ±5.5 d standard deviation. The model had extreme error in predicting hatch in British Columbia. A linear model predicted 50% hatch of summer-generation eggs in both Wisconsin and British Columbia to within ±1d standard deviation.