Sunday, June 19, 2011

Flies as Decomposers-Disgusting but Necessary

 Some of you may not want to look at all of these pictures. Seriously!

 A squirrel was killed by a car in front of my house this weekend, and I set it in the grass until I finished a short errand.  One half hour later there were flies all around it. 

So I set it on a table, like any normal person, so I could photograph the flies doing whatever they do.

I've seen this hundreds of times, but never really watched it up close.
 In this picture an alien-like fly peers over the edge and seems to say, "Are you dead yet?  Hurry up, I've got work to do!"

Squirrel fur is a thick forest to flies trying to find a place to lay their eggs. So they focus on natural entry areas, in this case, the mouth and nose. 

All of the flies present were the same species, as you can see in the pictures below, and the only thing they did was lay eggs.  For 6 hours.  In the nose and the mouth.

They pushed each other around and had no fear of the camera or me moving around.  It was like an affirmation of the CSI TV show.  One species of fly laid eggs for a few hours right after the squirrel died, then they left, and nothing else landed on the squirrel for the rest of the day.  How they knew the squirrel had just died is a mystery to me.

The female flies have a long tube at the end of their abdomen called an ovipositor.  The eggs travel down this "tube" and are placed where the female's instincts tell her to place them-in this case, inside the dead squirrel's mouth and nose. That will give her babies access to the soft tissue as soon as they hatch.

You can see the flies in these two pictures pushing their abdomens into the openings of the mouth and nose, and the following picture shows how these openings were completely filled with eggs. 

 In less than 18 hours all the eggs had hatched.  In this picture you can see the left over egg skins in the mouth.  The babies (maggots) have moved farther back into the mouth.  The larvae in the nose were actively moving around at 10 this morning.

While not a pretty sight, just think what it would be like if nothing ate these dead animals!  Flies are very busy cleaning things up for us and get very little credit for their unsavory jobs.
While the maggots were getting aquainted with their new living quarters, the flies returned, but not to lay eggs.  All day today, all the flies did was eat on the squirrel.  I didn't observe any egg laying.

Eating for these flies is not chewing out a chunk of flesh and chewing it up.  These flies have a fleshy appendage for a mouth with a sponge like blob on the end.  They push this around on liquidy surfaces and soak up their food.

You can see this fly doing just that on the squirrel's eye in this picture from 11 AM this morning.  These flies were wary and would not come close if I moved.
I took this picture at about 4 PM.  The baby maggots are packed into one side of the nose here like Penguins in the movie "Planet Earth."  What you see here is the tail ends of several hundred maggots all packed tight together.  I'm guessing they breathe through their tail ends, while the head end is chewing on breakfast, lunch, and dinner.  You can see two have been squeezed out and are trying to get back in.

I may not continue this investigation, as the smell will not be welcomed by others nearby, not to mention my own enjoyment of my yard.

Keep doing your stuff, decomposers, down wind if possible.


  1. Great photos Siah!

    My mom gave me your blog address, but I hadn't really looked at it until today....WOW amazing shots! What kind of camera & lens(es) do you use? I broke down and got a digital SLR (Canon T1I) about a year and a half ago....primarily for capturing good youth sports pix, but I tend to use it for everything now except on rainy days!

    Take care...Audra

  2. Hi Audra,

    You are the first comment I have tried to repond to, so I'll see if I can do this. Thanks for your comments. I use a cannon 50D SLR camera. Most wildlife is with a Tamron 500mm lens with some extension tubes to bring the picture closer. I have just started using a 180 cannon macro, and was trying to learn how to do the flash with it in this post on the flies.

    It is good to hear from you. Hope all is well with the family which looks like it is growing up! I'll try to look at some of your blog pics.


  3. why would you but a dead squirrel on the table that's not what a normal person do OK so do not do that no more and when the baby flies hatch you going to have flies all over your house and that's not normal dude

  4. Does it come with a side of fries? or is that just the lunch special?

  5. Hi! Do you know the flies are of what species? I'd like to use your story as an example for in my assignment.

  6. Hi! Great pics! I thought flies secreted a fluid that causes the flesh to liquify so they can then mop up the slushie stuff -yum! Debbie