You can get as realistic as you want but I have caught a lot of fish in a lake full of Crawfish using this fly on a fast sinking line (Depth Charge 300)
But I absolutely love this pattern for LM and Carp on a floating line
The weight at the rear is because crawfish swim backwards, so you want the jigging motion to be at the rear, rather than the front of the fly. Crawfish land tail-first when they swim.
I’ll try to submit it it as soon as I can get some time to do the tutorial. It would be cool if FAOL could post videos of patterns. That would be easier (for me, anyway…).
I think podcasts are an option on FAOL. LadyFisher can correct me if I’m wrong.
Ed
Good looking easy pattern from this site:
http://www.flyanglersonline.com/bb/showthread.php?44634-pine-squirrel-crawfish
Nice crawfish, but it’s not a fly. It’s a jig.
I tie jigs, too, as well as make my own fishing lures.
Is there not a fine and wavering line between jig/lure/fly? If you tie the pattern with bead chain eyes, bead, or barbell eyes it’s a fly even if you use a 60deg jig hook, one of my favorites. If you use a jig hook with the lead already on there and tie the same pattern, it’s no longer a fly? If I throw my pattern with barbell eyes on a spinning rod and you throw it on a fly rod next to me, does it magically change from a fly to a lure? Too confusing an argument for me, but it sure gets tossed about a lot.
I really like the links to some of those patterns. They should also be a great carp fly also. Great looking flies by all. By the way, if you watch crawfish in the water, when they burst away with their tail a’flippin, they close the claws together so it might be best to not lock the claws in an open position. 'Course, I don’t think that makes a lot of difference since in my fishing bass with heathen tackle I caught fish on craws that had lost both of their claws. If a fish wants, he’ll get it. I also learned something else both by feel and by sight. A bass often yanks a craw off the bottom and drops it. This way they can grab the whole craw in thier mouth and not have to try to get past the claws. If you’re fishing right on the bottom and get a bump, don’t set immediately. Lift and feel for weight. If he has it, he’ll hold it. If he doesn’t he might well grab it hard so be ready.
Well said vicrider, a couple of years ago I ran into a guy catching some nice trout using a Clouser minnow on his ultra-light spinning outfit.
Fishing a fly on a spinning outfit is …fishing a fly fishing/lure. Simple. Now, fishing a REAL crawfish on a fly rod, is BAIT FISHING…simple 
If the lead is molded onto the hook, it’s a jig. If it’s tied on, it’s a fly, if you fish it on a fly rod. If you cast it on a spinning rod, it’s spin fishing with a fly, just like using a fly with a casting bubble on a spinning rod. If you use live (or dead) bait with a fly rod (which I do sometimes), it’s fly fishing with bait. A lot of fly patterns can be tied on jigs, and as trailers on French spinners.
Well,
I do use these specially on a deep nymph rig and micro buggers
http://www.cabelas.com/product/Fishing/Fly-Fishing/Fly-Tying/Hooks-Hook-Storage%7C/pc/104793480/c/104721480/sc/104340780/i/103885380/Fly-Tying-Jig-Heads/744626.uts?destination=%2Fcategory%2FHooks-Hook-Storage%2F103885380.uts&WTz_l=DirectLoad%3Bcat103885380
But if yu don’t like the molded bead.
http://midcurrent.com/flies/hooks-the-jig-is-up/
I have an acquaintance that uses a fly rod, because of the length only, and just mono on the reel (relying on lead to get the bait or lure OR a water bubble 0ut)…not fly fishing to me, just plain ol bait fishing.
I don’t have a problem with a molded bead, or leadheads or anything. I fish with all of them. It’s just a matter of definitions.
I’ll even share one of my dirty little secrets…I sometimes put a spinning reel on my fly rod and use it like a noodle rod, for crappie and bluegills, with ultralite jigs, and worms. It never made sense to me to buy an Uncle Buck’s 10’ Crappie Rod, when I already have rods that are almost that long, and probably have better action. They work beautifully.
It may seem to be a muddle, but there is a very real difference to a game warden if you are fishing “flies only” water in many states. According to my guide, you can fish flies from a spinning rod in the “flies only” water on the North Branch of the AuSable River legally. (He told me several years ago.) The same cannot be said by fishing non-flies with a fly rod.
In many places, molded jigs are specifically excluded from the list of what is considered to be a fly, but bead-head flies are allowed. Working around fine lines should not trouble people who tie flies or use fine tippet material. 
Ed
I have said it before. The only definition that really matters is the one in the rule book that governs the waters you are fishing in and the opinion that matters is that of those that interpret said laws.
I personally watched a warden give a ticket in fly fishing only waters to a fly fisher that kept his leader in the water a couple times while changing spots in his canoe. The ticket was for trolling and you could visibly see the angler wasn’t intentionally trolling for fish.
With the above being said I routinely will use jigs and weighted flies on fly rod but I don’t consider myself fly fishing. I consider it using a fly rod to fish jigs. A micro jig on a floating line is a great way to manage depth control.
To get things back on track my favorite crayfish fly is a General Practitioner (GP’s), shrimp fly, with a couple extra pheasant feathers curving out along the sides to look like claws. I tie a lot of GP’s for striped bass so it is a favorite and I make the minor modification to make it appear crayfish worthy. Colors include the standard GP coloration to browns, olives, and blacks.
Like I said, it’s a discussion that could go on forever, and already has in many threads on many boards.
Taking a slightly different tack, last fall I went on a guided trip on the Roaring Fork River and the guide set us up with little nymphs, extra lead, and bobbers. 70 years old and this is the first time I ever had a bobber on a fly fishing outfit. Like the Gigman, I’ve used bait and spinning reels on a fly rod, but when I go fly fishing I’ve never carried a bobber with me. I hated it. We didn’t catch much for fish and my heart was never in it just watching a bobber and I did a poor job of line control and was tangling more on that trip than in last 5 years combined. I went along with it when I should have simply said, you take care of the boat and I’ll fish my way, since it was my money, but I tried to go with the flow. Somehow I just can’t associate bobber fishing with fly fishing but I guess it’s the way it’s done now. I’ll pass on that.
I don’t bait fish, spin fish, Ice fish. Just fly rod …S Reel…S and a bunch different type Fly Line…S. I guide, I catch fish, I use FLY jig hooks, and BOBBERS. Never touch bait, smelly jelly of any kind…I AM A FLY FISHER. No two ways about it. My choice, nothing wrong with other choices, just not for me.
I also don’t over analyze FISHING. It is what it is. OH, I also use Glow Bugs, SJW, and Fake Fingernail Flies…still a fly fisher.
The great thing about the Crawfish pattern I posted is the arms are rubber and the claw is foam. Great action!
Here are a couple for smallies
