Some years ago a friend of mine shot some video of caddis emerging, using a dissecting microscope. Sorry, but they are not available on line. What is quite amazing about them is how quickly they emerge. One second the pupa hits the surface, the next there is an adult on the surface. It really does take less than one second to emerge.
It is true that many adult caddis appear to "shoot" out of the water like little Polaris missiles. But remember- most species (not all) make the journey to the surface buoyed up by gasses trapped under the pupal shuck.
Gary LaFontaine is was the first to describe the rapid emergence of caddis in his book, Caddisflies.
I believe I am correct when I say that most entomologists and fly fishers who have studied caddis now believe that this is not the case.
The meniscus is a significant obstacle to emerging insects. The molecules of water are bonded together by hydrogen bonds because water is a polar molecule with a positive end of 2 hydrogen atoms and a negative end of oxygen, they line up like bar magnets. These bonds are weaker than covalent bonds but they are strong enough to float a steel needle and they are strong enough that water can pull itself up a tube with the capillary action provided by the hydrogen bonds.
There are some caddis that undergo pupation on the stream bottom so they go from larva—>pupa—>adult on the bottom and ascend as adults. But the majority of caddis must undergo the transformation from pupa to adult at the surface. They cannot do that and break through the meniscus in a second.
The best source of entomology for fly fishers is Troutnut.com. This is what they ave to say:
”Pupae of different species use three different methods to emerge:
• Most species rise to the surface and struggle through. They usually take flight quickly once they're out of the water, but slow species first struggle and drift long distances half-submerged as they wriggle free from their pupal shucks.
• The pupae of some species crawl out of the water on rocks, sticks, and such, so that the adults emerge high and dry.
• Some pupae rise to the surface and swim quickly across it to shore where they crawl out to emerge.”
”The speed with which caddisflies, the swimming type, ascend to the surface varies with the species, but it is doubtful if any of them rise like a rocket and shoot out into the air. A few accounts by entomologists describe the struggles the emerging insect goes through. For example, Dr. Cornelius Betten, in The Caddis Flies, or Trichoptera, of New York State, in a section written in approximately 1915, states about a common Spotted Sedge (Hydropsyche sp.): “I did not find the larvae but observed the pupae transforming on the surface of the water alongside of the government breakwater. . .” and in another section, “The pupae were caught as they were coming up for emergence alongside the government breakwater, but these specimens had doubtless been carried some distance by the swift current since they left the rocks.”
My studies of how trout feed on emerging pupae and my observations of the naturals also shed considerable doubt on the “rocket” concept of a caddisfly hatch. At least for those swimming emergers observed, including six important trout-stream families, my studies show that the ascent has definite periods of hesitation. It is the insect during these periods of hesitation that fly fishermen must imitate with their flies. They have to know where the pupae will pause and struggle before they can begin to fish a caddis fly hatch successfully.”
I have great admiration for Gary LaFontaine. I think if he were alive today, he would admit either that what he observed was atypical or misinterpreted by him.