Bee mimic flies in wild cherry blossoms

2010 May 29

Oh, the buzzin’ of the bees in the . . . wait a minute. Are those really bees?
We have a number of wild “choke-cherry” trees around the property which bloom pretty early in the spring, and back in the first week of May this one was in full bloom and was absolutely humming with bees. So, I went out with the camera to get some bee pictures[1]. Except, that upon closer examination, I saw that a large fraction of what were buzzing were not, in fact, bees!

The bee is one of our honeybees, but the other one is a bee-mimic fly.

And it wasn’t the only kind of not-a-bee in the tree at the time, there were also some of these:

Overall, I think that as much as half of the “bees” in the tree were actually bee mimics of various sorts.

And then, the next day, S_ presented me with one of our insect cages with two bee-mimic flies in it, and Lo! They were the same kinds as the ones I had photographed on the tree! So, here are some close-up pictures:

This first one looks to be one of the Helophilus syrphid flies. The adults come to flowers for nectar and behave a lot like solitary bees, but the larvae are another thing. They live in “organic-rich water”, which is something of a euphemism for things like raw sewage. They are related to Drone Flies, which have larvae that breathe through a long, thin snorkel that looks like a tail. I used to see lots of drone fly larvae living in the runoff from manure piles when I was a kid on the farm. S_ tells me that the local bait shops sometimes sell drone fly larvae as bait, labeled as “mousies”.

As for how to tell a bee from a bee-mimic fly, there are a few giveaways.
1. Bees have four wings, while flies have only two.
2. Flies have really tiny antennae, while bee antennae are larger.
3. Flies tend to have bigger eyes that cover most of their heads, and fly eyes are more likely to have visible patterns on them.
4. The bee mimic flies I have seen tend to have abdomens that are a bit flattened top-to-bottom, while bee abdomens tend to be plumper and more rounded.
5. Bees often have a thinner waist than flies.
6. If it stings you, it is a (female) bee.
But you obviously don’t want to depend on that last one if you can help it.

The other fly is the Greater Bee Fly, Bombylius major.

It is related to this bee fly that I posted last year, the main difference being that the Greater Bee Fly is bigger, has more dark hair on the body, and the leading edges of the wings are dark instead of clear. The lifestyles are very similar, though, with the larva being parasitoids of ground-nesting solitary bees.

In general, the various kinds of bee-mimic flies are actually pretty significant pollinators, along with solitary bees, bumble bees, and honey bees. The main advantage of honey bees and bumble bees relative to these other pollinators is that colony-forming bees are always available, while the flies and the solitary bees just emerge for a short period until they lay eggs, at which point they die off.

The Greater Bee Fly is something of a wash as a pollinator, because every bee fly that exists is only there as a result of killing and eating a solitary bee as a larva. So, one pollinator dies so that another can exist, and if there aren’t enough solitary bees around to do pollination then there won’t be enough Greater Bee Flies, either. The Helophilus fly, on the other hand, is a net win because the larvae can grow in any old puddle of “organic-rich water”. So, if you need pollinators, but don’t have access to/want to deal with honeybees, it seems to me that you could just cultivate some Helophilus in some rotting manure runoff and get as many pollinators as you want. And as an added bonus, they don’t have stingers!

[1] This is one of those cases where the digital SLR+macro lens really makes a big difference. In the past, whenever I tried using the old point-and-shoot to take pictures of bees on flowers, I ended up with a lot of pictures of flowers that had formerly had bees on them, because the time between pressing the button and taking the picture was long enough for the bee to flee. The digital SLR, on the other hand, takes the picture immediately when I press the button, which really cures that problem. The macro lens also lets me stand back a few feet while still getting reasonably large image sizes, rather than having to be practically right on top of the poor bee. And there is Absolutely. No. Way. that I could have gotten that picture of the bee-mimic fly in flight with the old camera.

4 Responses
  1. Ramsey Piotter permalink
    May 29, 2010

    those are some good close ups

  2. May 30, 2010

    Fabulous photos. Your new lens is taking this site to new heights.

  3. May 30, 2010

    Do the flies also hold their wings differently when they aren’t flying? I often think “bee” when the wings are more-or-less folded tightly to the body, and “fly” when they’re out at an angle. I don’t know if that’s really consistent or not, though.

  4. May 31, 2010

    You might be right, I’m not sure I’ve seen bees hold their wings out at an angle when resting. Although, not all flies do that, either. I know cluster flies fold their wings fully when they are at rest, and some other flies seem to have both a “fully stowed” position, and a “ready” position where the wings are out at an angle for rapid takeoff. Still, in combination with the other features, it might help. Plus, if the wings are out at an angle, it is easier to see whether there are only the two wings.

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