Butterflies are like all insects temperature sensitive and a changing climate with higher temperatures might affect their phenology. Several studies have found support for earlier flight dates among the investigated species. A comparative study including 66 species of Swedish butterflies in Sweden was undertaken and the result confirms that most butterfly species will now fly earlier during the season. This is especially evident for butterflies overwintering as adults or as pupae. However, the advancement in phenology is correlated with flight date and some late season species show no advancement or have even postponed their flight dates and are now flying later in the season. The result also showed that latitude had a strong effect on the adult flight date, and the majority of the investigated species showed significantly later flights towards the north. Species flying early in the season were more affected by temperature than species flying later in the season and species overwintering in their late stages (as pupae or adults) were more influenced by temperature compared to species overwintering in their early stages (as larvae or eggs). In essence, a climate with earlier springs and longer growing seasons seems not to change the appearance patterns in a one way direction. We now see butterflies on the wings both earlier and later in the season and some consequences of these understudied and complex patterns are discussed. So far, studies have concentrated mostly on early season butterfly – plant interactions but also late season studies are needed for a better understanding of long term population consequences.