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Tiny bubbles

I caught a fly blowing a bubble recently and recalled seeing some similar pictures here before. I thought I'd collect all the pictures I could find here into one place along with a link to another site discussing the behavior. There doesn't seem to be a forum topic about bubble blowing yet, or my search skills have failed me.

If anybody finds more pictures or interesting discussions or speculation, add a reply. One question I have -- is this behavior limited to certain families of flies?

Thread on

two more

Bump, a scarab
Today my flightless captive Cotinis mutabilis specimen was observed apparently bubbling. Shortly after being dropped on the floor, it defecated (I attribute this to fright, as annoyed specimens can squirt frass) and later blew a clear brown bubble while perched on top of a sheet with retracted antennae. After I left the room to get a camera, the bubble had apparently been swallowed (there was no stain under the beetle).

In the past, I have also observed C. mutabilis adults occasionally regurgitating liquids without bubbling for unknown reasons (sometimes this takes the form of "drooling" on food). However, regurgitation of any sort does not occur too frequently in the beetles, from my experience. This suggests that the bubbling incident may have been stress-induced.

A Lasioglossum bee

A few more
Frit fly (Chloropidae), after feeding on bird droppings

and two species of Suillia (Heleomyzidae) after feeding on a stinkhorn

and another frit fly, I think:

Bubbling bee

Another one
I have no idea on the ID of this fly, but it seems to be doing the bubble trick:

Tiny Vinegar Fly...

In addition,
several variations of Caelifera are also known to discharge internal brews ("tobacco juice").

I had a Polistes fuscatus male
and when I squeezed it's abdomen, it regurgitated a drop of liquid. Didn't get a picture, unfortunately.

I've seen spiders that also did this, but I don't know why they did it.

More bees


This candy-striped leafhopper was walking around with a big bubble of liquid. Someone explained to me that the leafhopper had just relieved itself of a bit of liquid and hadn't deposited it yet. I never did see it do that. I think this isn't a good example of bubbling. The person who explained this phenomenon said they eat so much plant material with a large amount of liquid buildup and so have to relieve themselves frequently. (At first, I thought it was to present to some ant as honeydew.)

not a fly

Here's one

For the moment, anyway.
It got frassed just now.

And a very small one

One More

David A Burke's nice one

Another fly

A marshfly, a very sweet flie, and a beetle

One more

Btw, both of my flies with clear drops or "bubbles" were rescued from the bird bath and may thus get rid of excessive water the drank/absorbed during their ordeal.

Another bee

Another example

Three more flies

Another thread about this...
on can be found HERE

-Disregard my previous post-
Thanks for pointing that out John. I guess I missed that link in the original post. Very sorry about that...

I think
that is the same thread as in the original forum post above.

On my image , MA Ebbert posted a link to the abstract of a paper that deals with this "bubbling" (apparently the accepted name for the activity) in Apple Maggot Flies (Rhagoletis pomonella, in Tephritidae).

It seems to be clearly a post-feeding behavior (at least in the experiments, although I didn't read the experimental setup in detail and don't know if they controlled for non-feeding flies). It also was correlated with ingestion of liquid foods (so dry-feeding flies might not exhibit the behavior). (Also correlated were temperature, volume ingested, and concentration of nutrients in the ingested liquid.)

If you have access to a good library, the full version of the paper (the link provides only the abstract) has an interesting discussion of what they concluded about bubbling towards the end. In a later paper (the reference is on my image page), the authors claim to have weighed the flies during bubbling and have shown that there is significant weight loss during bubbling. They have also observed flies depositing droplets on leaves and reingesting the droplet contents after the droplet dries. I haven't looked up or read the later paper; one day when I have more time I'll have to do that.

In the thread on (link is at the top of this thread), some people expressed doubt about the effectiveness of evaporation from these small bubbles...based on surface tension and the geometry (a sphere having the lowest surface area to evaporate from, for a given volume). That makes a little bit of sense to me.

So here's a variant hypothesis I'll throw out: many assume that making the bubble is a way of processing the food in the bubble. What if it is instead a way of processing the food left behind in the crop? Maybe water isn't being evaporated from the bubble, but finds its way out as a result of processing going on inside the fly, and this process maybe proceeds faster if the crop isn't full?

Neat discussion.

Mecopterans do it too

What could be more delectable than a dark brown blob of putrefied body parts that were probably dead to begin with? My guess is it's something like a cow chewing its cud.

it could be like a sort of waste management inside that goes outside the mouth way

Has anyone looked into commun
Has anyone looked into communication chemicals in these drops? Seems like it could be an advertisement methoid and the drops reabsorbed after a bit of air time to conserve moisture.

Adding image
I have an image to add here, but I don't see the "move tagged images" link when I get to this discussion. Can you help? I was so surprised to hear that the bubble is liquid contents from within the fly, because some bubbles are so clear they look like raindrops! You would think all bubbles would be at least somewhat opaque. (I'm just an armchair naturalist.)

We'll link to the image this way, and eventually when the fly gets an ID, we can move the image into the guide with the others in the same family.

To John R. Maxwell
I see. Thanks for moving it.

Bees do it too
I'll try to find some pictures. Lynette had some nice ones.
I understand that it is a way of making the nectar more and more concentrated. Also, as Eric said it may be used for cooling.
Here is one:


Lacewing blowing pearly-looking bubble

John Ascher left this comment on the above image: "it is evaporating nectar to concentrate sugars." This agrees with what some people have suggested here. Also, here's one more fly:

It comes with this comment, from Kevin Hall: "I seem to remember some discussion of various insects blowing bubbles on the Guide somewhere. One theory proposed was thermal regulation. Well... November. Washington. I don't think so. That's not to say that it couldn't be used for thermal regulation other times, but cooling off during the late fall here wouldn't do too well. Maybe it could be used for warming up??"

I have no idea if thermoregulation is part of the function, but certainly having less liquid in your body to keep warm makes it easier to stay warm.

What if having it out in the sun somehow warms the droplet up?
Could the droplet then serve as kind of an artificial heater. Kind of like drinking something warm when it's cold. I'm stretching here, I know.

Two more


More images


Another possibility
The black fly image reminds me of a behavior I've seen in mosquitos--one in which a mosquito extrudes one or more droplets of fluid from its anus after consuming a large amount of blood. I always assumed that it did so in order to lose weight before flying away. Might these flies (and other insects) be trying to "lighten their load" before taking off?

More more

"Vomit drops"
I have heard (or read?) these "bubbles" called "vomit drops," meaning they are regurgitated liquids. Note that the flies involved have the "sponging, lapping" type of mouthparts (Hey, get that bee fly out of there, it's messing up my hypothesis!:-). They regurgitate enzymes to help liquify solid food particles (at least that is my understanding). I also wonder if, in the absence of food, this "bubble-blowing" somehow figures in thermoregulation (cooling)? Now, why can't I get that Don Ho song out of my head....?

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