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Saturday, April 20, 2013

Deer Bot Flies at Lake Morena

After reading Margarethe Brummermann's blog post yesterday about bot flies, I became intrigued by the fuzzy, bumblebee-mimic deer bot fly pictured in the post:

Then I consulted Lynn Monroe's new book: "Desert Insects and Kin of Southern California: A Photographic Survey and Natural History - Anza Borrego Desert State Park" and became convinced that these bot flies might not only exist in the region, but that they might be out and about at this time of year.

So after meeting Gary's son Ted at the Mexican border to see him off on his Pacific Crest Trail adventure, Gary and I decided to take a hike at Lake Morena, convenient and close by. I did not really expect perfect "hill top" conditions (hill-topping is the habit of some insects of congregating at a high point like the top of a hill or mountain and often establishing territories, in an attempt to intercept passing potential mates). Bot flies are known for this behavior, and amazingly, after a false alarm, in which I thought a smaller carpenter bee was a bot fly (!), we actually FOUND deer bot flies perched and periodically flying about at a high point in the chaparral overlooking the lake!

Cephenemyia jellisoni, a Deer Bot Fly. This specimen was captured at Lake Morena, southern San Diego County, on April 20, 2013. 

Dorsal view of Cephenemyia jellisoni, deer bot fly. Lake Morena, April 20, 2013.
These flies do not feed as adults, but after mating, females will deposit tiny larvae in the nasal cavities of Mule Deer. The maggots can reach as much as an inch in length, and will develop inside the respiratory passages of the deer.  Later the maggots will be sneezed out, to eventually pupate in the ground and emerge as an adult fly. Apparently this does little harm to the deer, despite its repulsiveness to humans.

The "hill top" at Lake Morena. Rich chaparral habitat. 
Lake Morena, San Diego County, California.


  1. I was covering my nose the entire time.

  2. You don't look very much like a stag, Gary? These types of bots occur in Europe, too, and I can still see the picture of the throat of a dead (hunter-shot) deer, slit lengthwise, that showed a number of those maggots in situ. It was in a book with otherwise very beautiful images that I got before I could read and that's the only image that I remember exactly, not because I was so shocked, but because I had to have it explained to me by an adult (who probably WAS shocked)

    1. I've seen some images like that in the web in the last couple days, researching these guys, and it's amazing to me that such large creatures stay so long in the airway before being snorted out. Apparently even Aristotle observed them in slaughtered deer! I've definitely learned some new things here, and would like to find more species in the genus!

  3. We used to clean small yellowish eggs from our horses' fetlocks. Not easy, they cling. Horses like to bend their head and rub their faces against that part of the leg: the eggs and larvae of the horse botfly get into their nostrils and then the air way that way. If I don't imagine it (and it has been over thirty years since), I saw the bot fly throw its eggs at the horse's leg like a bee fly bombarding a bee nest: flying and dipping.

    1. Interesting! Yes, I read that they fling larvae into the deers' nostrils directly sometimes. Accurate little things!