I have witnessed what I call the "Reverse Hatch" of the caddis for many, many years. These are the female caddis who have returned to the water to oviposit their eggs beneath the surface and then rise back to the surface and fly away. I think this "reverse hatch" is what is often thought to be an actual hatch.
In trying to determine whether or not the Gary Lafontaine observance of gas bubbles in the ascending caddis pupa are real (Many current authors dispute his conclusion), I found this quote from Gary Borger back in 2010:
"The insects seen with a shining bubble appearance that pop to the surface and "hatch" in an instant are caddis females returning from egg laying. They dive or crawl to the bottom and lay eggs directly on the bottom (see Caddisflies in the archives). They carry an air bubble with them so they don?t drown, and when done, they swim to the top (assisted by the buoyancy of the air bubble; the air bubble bursts, and the adult flies off"
It is so odd to me that we don't seem to have conclusive, definitive proof in this day and age of such a relatively simple natural phenomenum as this.............