What's Up With The Caddisfly Emerger Bubble?


Gary LaFontaine claimed that some caddisfly emergers somehow create and air bubble and use it to emerge.
Supposedly, he said he had seen the activity while using scuba gear in a river. I've heard other aquatic entomologist dispel the notion. They claim that the bugs sometimes take on a shiny appearance when emerging but they don't go along with the bubble bit. The shiny appearance, they claim, may be what Gary saw and it wasn't really an air bubble. The shiny appearance may also explain why Gary's pattern works as well as it does.

I do know that some bugs will carry an air bubble with them when they dive subsurface but they do so because they are above water and in the open air.

I've given this a lot of thought and I'm having a hard time figuring out how a caddis can generate a bubble when it is subsurface. Sure, there is oxygen in the water and that's where their gills come in but for them to create a bubble to use to rise to the surface seems unlikely.

I'm on the fence. Is it fact or fiction that an emerging caddisfly generates a bubble to help it rise to the surface? Inquiring minds need to know :)


Staff member
Hi Gene,

Wouldn't touch this question with a 10-foot pole. ;) However, I will refer you to a renowned caddisfly expert who retired to Grants Pass several years ago, and can probably answer your question. Please see PM from me.


Active Member
It doesn't seem that unlikely to me. Some mayfly nymphs (Callibaetis for instance), as they mature toward emergence, somehow manage to generate gasses beneath their exoskeletons, making them more buoyant and forcing them to rise to the surface


Thanks, Taxon. I'll ring him up and see what he has to say.

All I know is that not all entomologists agree with Lafontaine so that intrigues me. Maybe the bugs do somehow generate a bubble to ride to the surface, maybe Gary was wrong. That is what I'm trying to find out.

zen leecher aka bill w

born to work, forced to fish
emerging chironomid pupa have a silvery look to them. It's gasses under the skin that "puff" the skin out so the adult can pop out easier. Probably the same thing with caddis. The adult diving caddis probably have air bubbles adhering to the skin, wings, hair, etc when they go underwater to lay eggs.


Bill, yup, the diving caddis most likely do have some manner of air bubbles attached when they dive underwater but Gary was talking about an emerger that had lived its entire life underwater before heading to the surface.

A caddis emerger using an air bubble to help it rise to the surface while yelling "yeeeeehhhaaaaa" all the way up is the point of contention.


Staff member
Will be interested in what Dave Ruiter has to say. As I recall, it may have been Ralph Cutter who speculated that Gary LaFontaine was probably observing diving caddisflies returning to the surface after having deposited their ova on the substrate, but given my enormous respect for the truly groundbreaking research on caddisflies conducted by Gary, I have trouble with subscribing to that theory.

EDIT: Ralph, please accept my sincere public apology for thinking it might have been you who doubted the accuracy of Gary's observations. Based on your post, I am obviously mistaken.
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In the time of chimpanzees, I was a monkey
Gene, I think I get it. You're talking about air bubbles outside the shell, not inside. That's different, and I have nothing to add.


It is unlikely that Gary would have confused an adult diving caddis with an emerger, they don't look similar so I doubt if he made that error. If he did error, I think it may have been the fact that some, but not all, caddis emergers have a shiny appearance and he mistook it for a bubble.

I've sent e-mails off to two aquatic entomologists of note, Dave Ruiter from Roger is one, so hopefully, I'll get a response from one or the other or hopefully, both.

We all know that Gary's patterns work so it doesn't matter if the bubble theory is correct or not from a flyfishing standpoint. We don't really know why many different patterns work but they do.


Update: I've e-mailed a number of aquatic entomologists and have asked them about the caddis pupa bubble bit and so far, all I've received in answer to the question of the ability of an emerger caddis using a bubble is "I don't know".

They all mentioned that a diving caddis adult that has been flying around in the open air does sometimes take a bubble underwater with it and uses the bubble to survive up to 20 minutes subsurface ... kind'a like the bug version of a scuba tank.

So maybe, Ralph Cutter is correct and what Gary saw was actually a diving caddis that had been underwater for a goodly amount of time so Gary mistook it as an emerger.

I have one more lead to follow up... if I end up with another "I don't know" then I'll give up on trying to find an answer to the bubble question.


Sculpin Enterprises
Very interesting topic. I don't see physiologically how a totally submerged insect can create a bubble outside its exoskeleton. [Excluding a diving caddis or backswimmer or diving spider or beetle which are capturing a bubble of atmospheric air and carrying it underwater.]

The process by which fish fill their swimbladder with gas is well understood. A few primitive fishes (herring and tarpon) gulp air at the surface and push that air through their mouth and esophagus via a narrow tube into their swimbladder (physostomous swimbladder) [and the evolutionary predecessor to air-breathing by terrestrial vertebrates]. This limits how deep they can swim because the gas, which provides neutral buoyancy, loses volume and buoyancy under increasing pressure as the fish swims deeper.

But the swimbladders of most fishes have no connection to the esophagus (physoclistous swimbladder). Specialized cells in the gas gland release lactic acid and carbon dioxide into blood vessels. This lowers the ability of hemoglobin to carry oxygen (Root and Bohr effects), releasing oxygen into the blood and into the swimbladder. The decreased pH also impacts the ability of the blood plasma to carry N2 gas. A unique blood vessel architecture (rete mirabile, see https://en.wikipedia.org/wiki/Swim_bladder) concentrates the lactic acid and CO2 and traps the gases until their concentration is high enough to diffuse into the swimbladder. The swimbladder itself is lined with guanine crystals which slow the escape of gas. This allows a fish to fill its swimbladder with low density gas to offset the density of bones and muscle and achieve neutral buoyancy. This typically requires a swimbladder that occupies about 5% of the volume of a typical fish. If a fish that is neutrally buoyant rises in the water column, the air in the swimbladder expands and the fish becomes positively buoyant. To compensate, another region of the swimbladder, the oval window, becomes vascularized and carries the extra gas away.

For any insect to create a gas bubble underwater, it would need to create a similar environment: a pocket which secretes acids, such as lactic acid and CO2, which changes the local solubility of gases in solution and which changes the oxygen-carrying capacity of hemoglobin or hemocyanin. A set of rete mirabile blood vessels would concentrate the acid and the gases locally. Not impossible, but I have not read of any studies that indicate these structures.



Steve, I'm leaning heavily toward our opinion. I'm not a scientist by any stretch of the term but a subsurface caddis somehow generating an air bubble never seemed quite right to me. I've been told by those who knew him as a friend, Gary was one great guy but I can't go along with his idea that an emerging caddis was using a bubble to rise to the surface.

His patterns do work but I don't believe it has to do with the fish seeing the antron as a bubble incasing an emerger.


Rowley also wrote a bit specifically in regards caddis on the same site, while he did mention something about gas and air involved with the change from larva to pupa (which I can see but I imagine there is more gas involved than air) he mentions this:

The majority of caddis lay their eggs beneath the surface by diving below enveloped in a shiny air bubble, a key pattern trait

This reinforces Cutters claim that Lafontaine most likely saw diving caddis with bubbles and not emergers with bubbles... which... at this point I'm inclined to believe.