Portraits of Wildflowers

Perspectives on Nature Photography

Freeloading

with 20 comments

Dark Fly, Dead Bee, Dead Spider on Tatalencho 8237

When I was happily photographing tatalencho (Gymnosperma glutinosum) at Wild Basin on October 27th I came across this little drama that I had trouble understanding. Most conspicuous was the dead bee whose head-down posture on the flower stalk made it look like an airplane that had nose-dived into a crash-landing. We have to assume the bee had met its demise thanks to the spider that now too was upside down and immobile, and that I took to be dead as well. Standing on the bee’s upraised rump was by far the tiniest of the creatures in this arthropodal ménage à trois, a dark insect that appeared to be biting or sucking the tip of one of the spider’s upraised legs.

I e-mailed for help, which came quickly. From entomologist Alex Wild at the University of Texas I learned that the dark little insect is “a freeloader fly (probably Milichiidae or Chloropidae, hard to tell from the photo), taking advantage of the spider’s kill. As Joe [Lapp] said, this is a fairly common phenomenon, but since the flies are so small it is often overlooked.”

I also heard back from local expert Val Bugh: “The spider is not dead, it’s busy eating and crab spiders prefer to remain still, especially when their prey blocks them from view. The black fly, commonly called a freeloader fly (family Milichiidae) is actually just standing on the bee’s butt — it only looks like its face is touching the spider’s leg because of the angle. Really, the mouth of the fly goes down and it is probably waiting to scavenge some droplets while the spider feeds (or it is wondering whether or not it needs to leave because there is a big, scary camera pointing at it). Usually, spiders and other predators just ignore these little flies, which might walk all over both the predator and its victim.”

Joe Lapp added some more: “I think I’ve only ever seen this once on the prey of a spider other than a crab spider. I think crab spiders are preferential because they don’t masticate their prey like most do. Instead, they inject digestive fluids into holes and slurp out the yummy insides. That leaves opportunity for flies to go to town unharmed. I wonder if the venom or enzymes also assist the flies. In my mind, the wild thing is that these flies show up before the prey begins decaying.”

So there you have the explanation for this curious sight.

———–

I’m away for a few days. You’re welcome to leave comments, but it may take me a while to answer.

© 2015 Steven Schwartzman

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Written by Steve Schwartzman

November 20, 2015 at 5:06 AM

20 Responses

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  1. A lot more goes on right under our noses (or lenses) than I would suspect.

    melissabluefineart

    November 20, 2015 at 8:45 AM

  2. Such a hairy guy.

    Jim in IA

    November 20, 2015 at 11:11 AM

  3. Your posts are just fascinating! I look forward to them every day — getting quite the education.

    Jenny

    November 20, 2015 at 8:15 PM

    • This one was quite an education for me as well, thanks to the knowledgeable people I quoted. And thanks for letting me know you look forward to these posts.

      Steve Schwartzman

      November 20, 2015 at 9:20 PM

  4. Interesting! Thanks!

    montucky

    November 20, 2015 at 9:01 PM

  5. La fotografía es buenísima, Steve. Te felicito.
    ¡Buen fin de semana!

    Isabel F. Bernaldo de Quirós

    November 21, 2015 at 5:13 AM

  6. Quite a “catch” Steve

    norasphotos4u

    November 21, 2015 at 1:06 PM

    • That’s how I felt, Nora. It’s one of the strangest things I’ve ever managed to photograph.

      Steve Schwartzman

      November 21, 2015 at 9:31 PM

  7. I’m way behind in reading blogs due to another virus so I’m sorry for my absence. What a strange and interesting situation to find, Steve! Thanks for sharing it as well as an explanation. 🙂

    Jane

    November 21, 2015 at 6:11 PM

    • I’m sorry another virus has slowed you down, Jane. A virus doesn’t inspire us, so may you soon discover how to recover.

      Steve Schwartzman

      November 21, 2015 at 9:37 PM

  8. Mind-boggling!!! What a mini-drama! I half-expected you to tell us at the end that the bee wasn’t even dead. (Which, of course, is what I assumed at first).

    Birder's Journey

    November 21, 2015 at 6:25 PM

    • Happy boggling to us all. The spider was hard to see, and then hard to believe still alive, but the bee had ceased to be.

      Steve Schwartzman

      November 21, 2015 at 9:40 PM

  9. Life on Earth (and most likely wherever else it may exist) is just full of amazement. Reading about insects is a lesson in this. There are so many unexpected strategies employed for the various functions. Their coexistence for mutual benefit is a great lesson for us.
    Super behavior image, Steve.

    Steve Gingold

    November 22, 2015 at 2:05 PM

    • The connections here are intricate, that’s for sure. If not for the three people I cited, I wouldn’t have understood the intricacy. Thanks for appreciating the image, Steve.

      Steve Schwartzman

      November 24, 2015 at 8:04 AM

  10. That is fascinating, thank you. I have photographs taken in Spain of a crab spider with prey that also showed up attendant little flies. I suspected the reason for their being there, but good to discover what they are. I love the common name you quote for them ‘freeloader flies’, most appropriate.

    theresagreen

    November 24, 2015 at 6:46 AM

    • You were ahead of me in seeing something similar, and even better, in suspecting what was going on. I’m glad my sources were able to confirm it for you.

      Steve Schwartzman

      November 24, 2015 at 8:38 AM


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