March Fly

2014 April 16

I found this mostly black fly with red legs on our dining-room window on June 6, 2013. Here it is on my fingertip, for scale:

It looks like one of the “March Flies” in the genus Bibio.

The wing venation looks right,

and it also has the characteristic spur on the tibia of the front legs.

Specifically, I think it is either Bibio vestitus, or Bibio xanthopus, both of which have the right coloration. B.vestitus is supposed to have a longer spur and less than 10 antenna segments, so I’m leaning towards that one.

The flies in this general family are known for emerging in large mating swarms early in the spring. Further south, this would be in March, but obviously up here it is more like May-June. This particular genus is more common in northern areas. This particular one is clearly a female, because the males have huge, bulbous eyes that are much bigger than the rest of their heads.

March fly larvae mostly live in the leaf litter, eating rotting things. The adults eat flower nectar, and so they are useful pollinators. They are particularly good for pollinating fruit trees[1], since they come out in large numbers early in the spring, right when those trees are blooming.

[1] Bees get all the press as pollinators, but flies do a lot of pollinating, too.

3 Responses
  1. Carole permalink
    April 16, 2014

    Nice piece. We have some flower flies that pollinate the paperwhites in the winter.
    Loved the video.

  2. April 18, 2014

    I love the red biceps on the fly. I can just imagine it saying, “Thanks. I’ve been working out.”

    As for the song, well, what could I do but throw you some linky love?

  3. Erin Hilley permalink
    May 9, 2016

    Thanks for your post. I just saw a pair of these flies mating on the branch of Amelanchier and your post was very helpful.

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