The Free Living Caddis ~ 4/18/2020

The free living caddis, also known by old school fly anglers as “the green rock worm”, is the most well known caddis fly, and also one of the most important food items available for trout. They prefer to live in swift aerated sections of cold water within a rich river system. They do not make protective cases of pebbles or organic material like most caddis fly larvae. No way, these critters are as tech as you can get. The two main genus I encounter are Rhyacophila, and Hydropsyche. Their body profiles are slightly different from each other, and also their behavior varies to some degree. This is the aquatic insect that really turned me onto the whole fly fishing/entomology world, so much in fact that my first brochure for my guide service featured a hand drawing of a Hydropsyche larva on the cover. Free living caddis is very prolific in all of our watersheds, from our valley rivers, to the upper Sierra freestones.

Hydropsyche larva is plump with a juicy green body, and a large blunt black head. I’ve seen them as large as a size 10 in the Blue River upstream of Dillon Reservoir in Colorado, and as small as a size 18 on the Yuba River. At the ends of their legs and at the base of their rear section is hooks that they use to cling to rocks. They are very well adapted to their environment. From the “Net Spinner” Family, they build permanent structures made of pebbles that serve as deflectors from the heavy current. In between these structures, they produce silk webbing that can be in the form of mesh fences, elongated tubes, and bags. These web formations collect algae, fine organic particles, and tiny insects that become food. Hydropsyche larvae lead a busy life of cleaning and repairing their nets around the clock. The adult is known as the Spotted Sedge (shown at the top of the post).

Rhyacophila are mostly plump in the mid-section of their body, and their head and rear are noticeably skinnier and tapered. Their bodies are various shades of olive, sometimes bright green, and their head is brown to black but much shorter than Hydropsyche. Rhyacophila is the purest form of the free living caddis, and are the most primitive representatives of that order. They also use their own silk as well, but as an anchor line like a rock climber rappelling down a face of granite. That’s some really cool evolution right there. In his book “Caddisflies”, Gary LaFontaine discusses his increased success fishing with net-spinning caddis larva patterns when he colored the last 18 inches of his leader white to suggest this silk anchor line of the natural. That is so Gary, always thinking so far outside the box, that the box didn’t even exist. Most are predacious, but a few will eat organic material being scavengers. When I sampled the Yuba River for aquatic life after the huge water events of 2017, these caddis larvae was always the first to appear in the samplings. They are very hardy and resilient. The adult is known as the Green Sedge.

The larva, pupa, and adult forms of free living caddis make up a very high percentage of a trout’s diet. Often it is the most where populations are prolific. Because the larva is so actively working and feeding, they are susceptible to being dislodged and thrown into the drift. A trout also has a good chance of eating them when they are in their behavioral drift, meaning the larvae periodically crawl out of their shelters, let go, and drift downstream 40, 50, or even 100 feet, thereby relieving competition and allowing the colonization of underutilized areas. This activity occurs on a daily cycle, and peaks near sunrise and sunset.

While living in Breckenridge Colorado in the early 90’s I kept finding samples of Hydropsyche in the Blue, South Platte, and Arkansas watersheds – Like a lot! I didn’t have a fly to copy, or the luxury of the internet to comb though, so I just laid out my tying materials with a specimen in a test tube of alcohol, and went to work. Immediately the pattern was a success. My good friend and fishing buddy Chris Fukuchi @shogun_of_denver and I caught so many nice trout on that first pattern. He called it the Killer Green Bug, which morphed into the KGB caddis. It quickly spread within our tight knit fly fishing crew in Breck including the fly shops, and about a year later there it was in the Orvis catalog “Killer Green Bug”. I was not even fazed due to my relentless pursuit of fishing 24/7. I simply didn’t care. Another great tip from Gary and aslo featured in his book “Caddisflies”(which you should all own, if not already) “A good imitation of a Rhyacophila larva is going to catch a lot of trout in swift, bouncing stretches of a stream. The same fly is going to do poorly in slow areas of the same stream. A fly fisherman can avoid wasting time in the wrong sections of a stream by working leap-frog fashion instead of in a straight line. If he is using an imitation of a fast-water insect he should fish only the swift, broken currents, skipping past the slower current areas. Likewise, if he is using an imitation of a slow-water insect he should only cover the quieter pools and flats.”

Like all my patterns, over the years I’ll change materials, details, and some innovative features. Some of the changes shine and some fail after extensive testing. I added an emerging wing to the KGB, an idea I got from Dominic Traverso’s Serendipity fly. I actually got to hang out with Dom one time at Fort Fitzwater on the Fall River. He had some new super tech emerger patterns he used for droppers off a dry fly that he shared with me back then. I still haven’t seen anything like them, and you won’t see me posting pictures of them either. 

I tried a bunch of stuff to make the free living caddis look more real, but in the end the pattern I use today has been the best. A plump green body with segmentation, whitish feelers at the rear, a big black head, and rubber legs is really all you need. In my opinion, these are the key elements that induce the trigger mechanism for a trout to strike when seeking free living caddis larvae in the drift.

Here are some tips when tying your free living caddis patterns. For sizes 10-14 use medium V-Rib, for sizes 16-18 use the small size. The end of the V-Rib material can be bulky when applying it onto the hook. I like to cut the end of the material at a 45 degree angle so there is a thinner section to tie on. One of the really cool innovative ideas I had when first tying this pattern was to wrap the hook shank with lime green krystal flash before wrapping the V-Rib. Being that the V-Rib is clear with a pigmented color, the krystal flash reflectiveness punched through, and the overall color glowed. I’ll take a brown sharpie and coat the top of the Krystal flash before wrapping the V-Rib so it is darker than the bottom of the fly, making it look just like the natural. You can experiment with different colors of flash to get the custom look you desire. When it comes to putting on the legs with the rubber floss, I will take my bodkin and split the material in half for a smaller size so it looks more natural and not so bulky. Lastly coat that big black head with clear nail polish for a wet glossy look.

Recipe:

Hook: TMC-2457 #10-18.

Thread for body: olive (8/0 for small patterns, 6/0 for larger patterns)
Thread for head portion: black (8/0 for small patterns, 6/0 for larger patterns).
Body: Larva Lace V-rib. 
Under body option: lime green krystal flash.
Legs: J Fair rubber floss, olive.
Tail hooks: white antron fibers