I've tried a good number of fly patterns on the crappies around here. Almost everything will catch fish at times, but there are a handful of patterns that have REALLY stood out as being VERY effective for crappies.
Crappies everywhere have a ritual of moving both higher in the water column AND closer to shore in the evenings. During the day they often hang in deeper water, and are more difficult to target with a floating fly line. But in the evenings they can often be caught fairly easily if you find the right areas.
Also be aware that although crappies often like to hang near some sort of structure (preferably woody structure, like a fallen tree or flooded brushpile), they often also school suspended in open water. Fishing can be quite good if you can keep near a school of crappies!
Another thing to keep in mind is that crappies prefer to feed UP. Depending on the water clarity, they will move up a fair distance to take a fly. I've seen this behavior even in cold water, when ice-fishing. I've seen crappies move up from 5' to even 10' below the fly to chase it upwards before hitting it. And that was in water of questionable clarity!
In the evenings, crappies can sometimes be caught on topwater flies, but I don't believe this is the BEST option.
I do a lot of my crappie fishing in the late evenings...from just before dusk to well after dark. The fly that has worked best for me when fishing at night over several years, is the Boa Yarn Leech. Silver or white can be good, but bright yellow has worked the best for me. This pattern has excellent movement in the water, and can be fished shallow and slow. Slow is key. I tie Boa Yarn Leeches unweighted on a #8 3XL Streamer Hook. If the fish won't come up to within 5' of the surface, you can add a beadhead to get the fly down a bit deeper.
Another unweighted pattern that can be good is a charteuse-and-white Thunder Creek Minnow pattern. The key is to have the right size fly. I sometimes go as big as a size 6, but usually size 8 and 10's will get more hits. And this is interesting...I've caught good numbers of 12"+ crappies using spinning gear and 3" long twister-tail jigs...but when fly-fishing, I've had better luck going SMALLER!
The top fly below is a Thunder Creek Minnow. The other hairwings sure look good, and I have caught fish on them, but just not nearly as many.
For weighted patterns, I've got 3-4 good ones in my arsenal. First is what I call a Microjig. These have marabou tail and chenille or yarn bodies. The best colors for me are pink-and-white, and chartreuse. I tie these on 1/80 oz and 1/100th oz jigheads, and sometimes larger/heavier if needing to fish deeper or get a faster sink rate.
A very similar pattern is the Springbrook Wunder. These are usually tied in more natural colors, starting with grizzly chickabou tail, and a silver or gold sparkle chenille body:
Here's the actual one that caught a lot of the nice crappies in the previous blog:
The next pattern is a Kraft Fur Clouser...which is tied like a Clouser Deep Minnow. Because I tie these in sizes 8 and 10...and sometimes even 12...I find Kraft Fur works a lot better than bucktail on patterns this small. 1"-2" sizes work very well. I've caught crappies on all the colors below. Chartreuse and/or white is always a safe way to go, size seems most important. Choose the barbell, hourglass, or beadchain eye size/weight to suit the hook size and the sink rate you desire. Also, you can somewhat affect sink rate by how thick you tie on the Kraft Fur. Too much can hamper hooksets, though.
Red sandwiched between white has been a good color scheme for me, too.
Somewhat similar to the Clouser, and also very effective, is the Crappie Candy. Again, pink-and-white or chartruese-and-white are usually good colors to start with.
One last pattern to consider, especially in dingy water is a minnow pattern tied with silver or opalescent mylar tubing, and your choice of tail material. You can use lead tape or lead-substitute wire under the mylar tubing to achieve the sink rate you desire.
If you feel comfortable with Woolly Buggers, weighted and unwieghted versions can work in a pinch.
Of the ones I've listed above, my top 3 would be Boa Yarn Leech for the shallowest presentations, and I really really like both the Microjigs/Springbrook Wunder, and the Kraft Fur Clousers. All three of these are very quick and easy to tie, which is a plus. If you are fishing around brush, you definitely might lose some flies!
You can use a strike indicator and fish somewhat vertically. In this case, the Microjigs are most likely to sit horizontally in the water, and so look like the most natural presentation. Wind/wave action on the indicator will provide movement to the microjig. If not using an indicator, I usually cast out, let the fly sink to an appropriate depth, then start a slow, jerky retrieve. For some reason, Crappies LOVE a jerky retrieve! Sometimes this can be better achieved by sort of shaking your rod while slowly retrieving, but often just doing very short, abrupt movements while stripping in the line works well.
As for strike detection, crappies often just suck the fly in. You'll really need to watch your line. At any indication that some extra weight is on the line, or your line begins to move backward while you are doing your slow retrieve, SET THE HOOK. A quick hook-set is more important than a STRONG hookset. Just tightening your line, or doing a medium side-sweep with your rod is usually sufficient to bury the hook. Don't horse the fish too much during the fight. The skin around their mouths is paper-thin, and you can rip the hook right out of their mouth with too much pressure.
Crappies on fly gear are a lot of fun! Good luck!