This is difficult, especially as Vince placed no restrictions on subject and I photograph lots of natural history subjects beside butterflies. Sticking with the 'preferred' butterfly theme, the highlight for me in 2013 was a trip in search of the Large Heath.
I only had a few photos of this species, taken many years ago (1992) at Meathop Moss. I decided that it was time to get some digital photos, so decided on a trip to Whixall Moss, on the Shropshire/Welsh border. It was bright and sunny when my wife and I arrived on the Moss but, although I could see my target flitting over the boggy ground, none came within range of even a telephoto lens wielded from dry ground!
After a while, we set up 'camp' at a likely spot on one of the paths and waited. Amazingly, a pair started courtship within a few feet of where we were sitting! I even managed to get shots of the elusive upper-sides of the wings. After that, everything seemed to 'come right'

and I collected more shots of a seemingly bomb-proof individual basking on a bracken frond. The weather then started to cloud over and it was raining before we got back to the car-park.
After that success, we continued into Wales and, on the following day, enjoyed a trip to the summit of Snowdon on the heritage steam train, under cloudless skies with brilliant visibility.
The weather was holding so well that we decide to return home through mid-Wales and take in a stop at Cors Caron NNR (Tregaron Bog). History repeated itself, in that we only saw distant examples, flying over the bog far from any firm paths. Then, as we were walking back to the car-park, I spotted a dry track leading off the main board walk, which seemed strangely similar to the location where I had had success at Whixall.
A few yards down this track, I spotted a single individual resting in the late afternoon sunshine, and allowing me to take several photos, including the one shown below:

- Cors Caron NNR - 12th July 2013
Nikon D300s with 70-300VR lens - 1/180s@f/8 ISO400
Overall a remarkably successful and satisfying trip.
Mike