The spiny ash sawfly, Eupareophora parca (Cresson, 1880), was discovered in Edmonton in 2003 at the Northern Forestry Centre defoliating planted ash trees (Fraxinus spp.). This represents the first record of this species from Alberta. Observations of adult and larval behaviour and life-history variables such as adult flight, number and duration of larval instars, and overwintering were made. The nature and severity of defoliation was monitored in 2003 and 2004, and large increases were detected in the amount of defoliation per site and the number of sites defoliated between years. The precipitous increase in severity and extent of defoliation indicates the possibility that this species could become a significant urban pest in the province.