The Figeater Beetle And The Fly

You may enlarge any image in this blog by clicking on it.  Click again for a full screen image.

About a year ago I posted an image that is very similar to today’s image.  I think that this one may be a bit better, but it’s a question of taste, I suppose.  It’s possible that some may not like either of them.

I was standing in the shade of a large mesquite tree in the riparian area of Sabino Canyon a couple of days ago when I noticed a Figeater Beetle dining on  a mesquite bean pod.  Figeater Beetles are large scarabs, more than an inch long, that show up in July and August in southern Arizona.  They make a very loud buzzing noise when they fly and they look a bit intimidating,  but they are harmless herbivores.

The beetle had chewed on the outer husk of the bean pod, causing it to leak sap.  As I photographed the beetle, I saw a small fly appear and land facing the beetle, just a fraction of a millimeter away. The fly drank the sap that was oozing from the wound caused by the beetle.  The two of them dined together in harmony.

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This is the second year in a row that I’ve observed this phenomenon and it caused me to wonder: how does the fly know to hang out with the beetle?  It cannot be mere coincidence that these flies show up whenever there are Figeater Beetles dining on mesquite beans.  One possibility, of course, is that the flies stay in mesquite trees out of instinct, and are thus available to take advantage of the beetles’ endeavors whenever the beetles show up.  That strikes me as pretty inefficient.  There are a lot of mesquites in our desert and not that many Figeater Beetles.  So, many flies would have to wait an awful long time in order to get a meal, if they ever got one.  Another possibility is that the flies follow the beetles.  That strikes me as more plausible and certainly a much more efficient way of getting a meal.  But, that raises another question.  How do the flies know to follow the beetles?  Is this instinctive behavior or is it learned?  I can’t answer that one but I think that the relationship between these two species is pretty remarkable.

Image made with a Canon 5DS-R, 180 mm f3.5L Macro lens assisted by Canon 600EX-RT Speedlite, camera and lens supported by monopod, M setting, ISO 160, f11 @ 1/160.

4 responses to “The Figeater Beetle And The Fly”

  1. Tom Munson says :

    Cool shot, Steve. Especially with the small fly.

  2. tkiiatmindspringcom says :

    This is an amazing photograph!

  3. Victor Rakmil says :

    Wonderful post and photo!

  4. Paule Hjertaas says :

    or the plant releases a smell when injured and the fly zooms in on that.

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