Two Blue Flower (or Hover) Fly Species!
Just less than a week ago I posted about Some Large Flower (or Hover) Flies, ending with the pièce de résistance, a large blue flower (hover) fly identified as Megasyrphus laxus. The photo above is not one of my best but it is from the same encounter with the fly on the McIntosh Run in Spryfield on August 19th illustrated in the previous post. Note the abdominal pattern, especially that the blue abdominal spots wrap around the sides and meet the midline, that the hindmost two spots meet in the center, and the light non-blue line separating the terminal black segments. Denis Doucet from New Brunswick wondered how late in the season these flies could be found and I thought I could provide him with an answer. I had photographed some blue flower (hover) flies in early October 2013, except...
...the ones that I photographed on October 11, 2013 at Roaches Pond in Spryfield are NOT Megasyrphus laxus! It turns out that ALL of the photos of blue flower (hover) flies I photographed last year, at three different locations between mid-August and October 2013, are of Didea alneti, a completely different species. Note again the pattern of blue spots on the abdomen. The spots on D. alneti do not reach the midline at the side of the abdomen, the hindmost spots do not meet in the center, the pale line separating the last abdominal segments is missing, AND the foremost and hindmost blue spots are a completely different shape. Nova Scotia has two different species of blue flower flies! Cool, huh?
Added Note: Andrew Young from the Canadian National Collection of Insects, Arachnids and Nematodes (CANACOLL) has confirmed that this second blue Syrphid is Didea alneti and not Megasyrphus laxus. Second Added Note: The photo above is of a male D. alneti. My earlier encounters with this species in 2013 were both of females (difference is that the hindmost spots DO appear to meet in females but not in males, see this reference with the illustrations.)