Phantom Crane Fly

2012 February 22

This one abruptly appeared in the house on August 14, 2011 (Sandy said she saw it come in through the front door with her, but wasn’t able to catch it). It finally settled down on the kitchen window for photographs.

This is clearly a Phantom Crane Fly, Bittacomorpha clavipes. There is nothing else quite like it, at least not around here.

It’s rather striking and easy to spot, which would make one think that it would get eaten immediately. It is possible that it is just distasteful, but that would be pretty unusual in a crane fly.

I think it is more likely that they are using their feet as decoys. The bulge at the end of each foot actually is big enough that it looks like an insect itself, while the leg proper is thin and hard to see.

When it flies, it looks like a tight swarm of up to seven small flies, rather than a single large one. The legs obviously come off pretty easily; this one is down to four. It looks to be missing both the rear left and the middle right legs.

So, as this crane fly flies along, anything that tries to catch it out of the air is more likely to snatch off one of the expendable legs than to get hold of the body proper, allowing the fly to escape. And if it happens to blunder into a spiderweb, it is likely to be able to just sacrifice a leg or two to the web and fly off. The crane fly can obviously manage just fine with four legs as long as it has at least two on each side, and I’ve seen some other crane fly species in the past managing with just three. In fact, since they only use their legs for perching or hanging, not walking, it would not surprise me if they could get along with just two in a pinch.

Incidentally, while the Phantom Crane Flies are true flies (Diptera), they are in a small family of their own (Ptychopteridae), completely distinct from the other crane flies (Tipulomorphs). Phantom crane flies are often found in or near swamps, and have aquatic larvae.

5 Responses
  1. Carole permalink
    February 24, 2012

    Thanks for helping me identify another insect. I’d taken a picture of one in the garage and never tried to identify it. Great information and through the link I learned mine, which was down to 4 legs, was a female.

  2. February 25, 2012

    Why is it called a “phantom”? Because it’s not in the same family as the rest of the other crane flies?

  3. February 26, 2012

    Carole: It’s starting to sound like these flies rarely have all of their legs!

    Anne: These static pictures don’t really do it justice, but when it was flying, it was really hard to focus on. It looked like this hazy, ghostlike blob floating through the air. It’s too bad I don’t have a video of it, it was really kind of startling how, well, “diffuse” it seemed to be. I expect that’s where the “phantom” name comes from.

  4. Bridget permalink
    February 27, 2012

    I know you’re not supposed to do it (natural selection and all), but I rescued a small crane fly from a spiderweb recently.

  5. sandy permalink
    February 29, 2012

    Bridget: No guilt! Confounding natural selection, I’m proud to say, is something humans are good at and have been doing for thousands of years!

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