A few days ago while I was walking in the Opal Natural Area, I noticed some movement in a small pit in the sand on the trail. Whatever it was, I could not distinguish it from the bits of burnt wood and pine needles that had also collected there. As I drew closer, it flew away, but I managed to spot where it landed on the trail’s edge. It quickly began the same movement that first caught my eye, and as I crept slowly forward, I saw what it was and what it was doing.
I love the robber flies (sometimes called Assassin flies) which are as fierce a predator as can be found in the bug world. I rarely see them, and when on the rare occasion I do, I usually have not been able to get a good photograph because they flee so readily. I know this is not always the case, because there are many fine images of robber flies on the web, but I have not had much luck with the few specimens I have come across.
After I managed a few pic’s of the egg-laying process, she moved on again. This time, she took a more typical stance, and allowed me to move in tight to capture her image while she rested,
C. falto at rest.
Thanks to John Acorn and Robert Cannings for the ID. Dr. Cannings also provided the following information:
Your robber fly is Cyrtopogon falto, a female. This species ranges across the continent from BC to Nova Scotia. It lives in sandy areas in forests and is the most common Cyrtopogon in the forests of eastern Canada. It’s not quite as common in the West, but there are numbers of records from BC and the prairie provinces. It seems reasonably common in the Edmonton region. Adisoemarto calls it Cyrtopogon distinctitarsus in his 1967 paper on the Asilidae of Alberta, but the correct name is C. falto.
Although a bit dated, the best site for learning more about this family of flies is Robber Flies (Asilidae) by Fritz Geller-Grimm.