Recent increases in global temperatures have contributed to advancing phenology of plants and animals. These increases in temperature have been shown to affect the phenological phases (phenophases) of plants and birds in Ireland, but less is known about the effect on the phenophases of Irish insects. Records of the flight periods of 59 species of Irish moths over the past 35 years (1974–2009) were obtained from a public monitoring group. Observations were analysed across the country using generalized additive models (GAMs) weighted by total yearly population numbers for each species. The results of the statistical analyses showed that 45 of the 59 species studied have a significantly earlier first sighting date now than when observations began. With this earlier emergence, 44 of the 59 species also have a significantly longer flight season over the same 35-year period. The extent of these changes varies across the country and by species life history. In particular, species emerging in spring are advancing at a much faster rate than species emerging during the summer. Many of these changes in first sighting are negatively correlated with rising temperatures in Ireland, particularly in late spring and early summer (May and June). The variation in phenological advancement in the moth species of Ireland is extremely complex and may be influenced more by species life history than by the phenology of interacting species, such as host plants.