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3. Caddisflies darkening after emergence

I don't know why I never really realized how common this was before. I guess I wasn't paying caddisflies much detailed attention until recently, but in my last couple trips I noticed how dramatically some of them change color in between emergence and egg-laying.

The apple caddis / shadfly on the Delaware system (Brachycentrus appalachia) is the example that really caught my eye, although now that I'm looking closer I've noticed it's happening to most caddisflies I've caught lately. The apple caddis has very light tan, almost white wings when it emerges, along with a bright "apple green" body. When I got mine home to photograph, I found that they had all changed -- they now had light gray wings, and their bodies were a darker evergreen color.

This was kind of a "duh" moment for me, since it's the sort of thing I should have noticed much earlier, especially since I know it happens with some mayflies. The obvious conclusion is that the color for egg-laying adult imitations must be quite different from that of emerger imitations (and that most of the photos on this site are useless for determing the color with which to tie emergers).

So, for those who have been paying attention to this since before I started fishing: is this something that happens with all caddisflies? Have you got any related tips?

Jason,

This happens not only to caddisflies, but to most emerging insects. Although the color changes are much more dramatic in some, most freshly emerged caddisflies, stoneflies, and mayflies display this to some degree. Your recent observations about the color of a freshly emerged stonefly and your photographs of appalachia (underwater shots of emergence vs. aged adult) show this clearly.

Jason,

I have also noted the changing color in adult caddis flies in Brachycentrus sp., Rhaycophia sp., and Hydropsyche sp. from the Southern and Central Sierra Nevada. It seems to be more manifest in the darker colored species, and appears to occur with quicker timing in warmer weather. It is possible that our local Glossosoma sp. also show a changing color, but their appearance so late in the day has made it impossible to witness this with certainty. My observations have all been in smaller streams above 5,000’. The specimens observed have all been captured onsite, not reared artificially. Just as an idle thought I would be interested to know if night emerging species would show the same coloration change during hours of darkness, or if they wait until sunrise.

Gonzo makes a very good point. Most insects experience this color change. Have you ever seen a newly emerged cicada? They are white and pale pastel colors. Then they become black and otherwise more vividly colored. Butterflies and moths don't show this as much, due to their scales, but most other insects do. When an insect is newly emerged, pale and soft, it is said to be "teneral."

There was an article by Thomas Ames, Jr. in a recent issue of Fly Fishing and Tying Journal in which his photos and narrative described the very phenomenon you describe, i.e., newly emerged aquatic invertebrates appearing pale orange, green or cream colored, but then darkening considerably within a few hours. (He also noted that many newly emerged caddis and stoneflies hold their wings upright to dry and harden, giving them an appearance that looks all the world like a newly emerged mayfly dun.)

It might be for these reasons that Ralph Cutter's E-C Caddis -- with its two-tone rust and bright green body, along with and upright wing -- is so effective.

Good point, Dave. Many caddisflies do hold their wings vertically when they emerge. Stoneflies often do this too, but since most emerge out of the stream, the resemblance to upright-winged mayflies is probably less significant from an imitation standpoint. The darkening often occurs much faster than a few hours. It can happen within a few minutes in many cases, though darkening may continue for some time.