This will be a familiar butterfly to those living in the UK and Europe. This species was first found in North America just outside Montreal, Quebec, in 2005. Since then it has spread first to the Ontario/Quebec border in 2012, and then to southern Ontario where it is now quite common. So far as I know, no records have been reported from the Ottawa region. I found a faded female on June 21, not far from the Ottawa River, and today, in the same general area found this quite fresh looking male. I think these two observations represent the first record of the species in Ottawa.

The common blue is associated with the European Bird's foot trefoil on which it lays its eggs. The site where I found the two butterflies has abundant populations of this plant.