Ask ten permit guides what’s in their box and nine of them start with the same word: crab. The permit crab fly isn’t one specific pattern — it’s a whole family of flies built around the same idea, because crabs make up the bulk of what a permit actually eats. Get the crab fly right and you’ve solved most of the problem before you ever make a cast. Get it wrong and no amount of good presentation saves you.
This is a rundown of the patterns worth carrying, and (more importantly) how to pick the right one for the water in front of you. For technique (how to present a crab fly once it’s tied on), see our guide on how to catch permit on the flats. This one’s about the fly itself.
Why Permit Eat Crab Flies
Permit have crushers in their throats instead of teeth in their jaws, which is why they can grind through a crab shell without needing to bite down hard. That anatomy shapes the whole design brief for a crab fly: it needs to look like something that’s trying to escape by diving for the bottom, sit still and believable once it gets there, and survive a permit’s initial mouthful without pulling free before you can set the hook. Every pattern below solves that problem a slightly different way.
The Permit Crab Fly Family: Patterns Worth Carrying
Del’s Merkin is the pattern that started the modern era of permit fishing. Del Brown and Captain Steve Huff developed it in the mid-1980s using Aunt Lydia’s Sparkle Yarn tied perpendicular to the hook shank and heavy lead eyes, a combination that makes the fly dive claws-up when it sinks, exactly like a fleeing crab. Brown landed more than 500 permit on his own Merkins over his career. It’s still the fly most guides would grab if they could only carry one, tied in tan and olive, sizes #2 to #6.
Strong Arm Merkin is a newer variation (developed by Nathaniel Linville and tier Dave Skok) that’s become a tournament standard in the Florida Keys, placing first or second in eight of eleven recent permit competitions. A single chenille claw off the back doubles as a stabilizing keel, and the fly casts a little lighter than a traditional Merkin, useful in calmer conditions where a heavy fly lands too hard.
Raghead Crab, developed by Key West guide Jan Isley, is one of the most versatile patterns in permit fishing and does double duty on bonefish when permit aren’t cooperating. It shows up in a lot of Xcalak fly boxes for exactly that reason.
Bauer Crab was built specifically for Belize and Yucatán-style flats. Its McFly Foam body absorbs water and sinks fast, which matters when you’re trying to get a fly to the bottom in turtle grass before a tailing permit moves off. Given the turtle grass flats on Chetumal Bay’s ocean side, this is a pattern worth having in the box here specifically.
Avalon dominates Cuban permit fishing on the strength of a bead-weighted keel that keeps the fly from spinning mid-flight — a small thing that matters more than it sounds like it should, since a spinning fly is an instant refusal for most permit.
Our guides also tie and fish Beck’s Fleeing Crab, Strong Arm Merkin, Casa Blanca Crab, and Tommy’s Floating Crab — a hand-tied sargassum crab pattern built specifically for the weed mats that show up on Chetumal Bay’s flats in April and May. For the full breakdown of what to pack and in what quantities, see our Xcalak packing list.
Weight Matters More Than Pattern
Permit feed on the bottom. A crab fly that doesn’t get down to where the fish is actually looking doesn’t get eaten, no matter how good it looks doing it. This is the single most common reason a well-tied fly gets ignored.
The rule of thumb: heavy tungsten or lead eyes for water deeper than five feet or moving current, medium lead or bead-chain eyes for the one-to-three-foot range most flats fishing happens in, and light bead-chain for skinny, tailing water where a heavy fly lands like a rock and spooks the fish before it ever gets a look. Some serious permit anglers weigh flies on a kitchen scale so they know exactly how fast each one sinks in a given depth, that’s how much this one variable matters.
This is also where Chetumal Bay’s mixed habitat comes into play. A single day here can take you from a sheltered lagoon in two feet of water to a deeper open-bay flat holding a bigger school — two different presentations calling for two different weights in the same fly box. We’ve written more about why Chetumal Bay’s flats fish differently from typical Yucatan water if you want the full picture of why that range of conditions exists here.
Match the Fly to the Bottom, Not Just the Fish
Color selection comes down to one question: what does the bottom look like where you’re casting? Tan works over sand and light mud. Olive or brown blends into turtle grass and darker bottoms. Cream stands out less over bright white sand. A small contrasting element (an orange leg tip, a chartreuse thread head) can trigger a strike without spooking a fish that’s studying the fly, but the overall rule holds: ninety percent natural, ten percent attractor.
Chetumal Bay’s habitat diversity means this matters more here than on a single-bottom-type fishery. The bay runs from soft mud in the backwater lagoons to mixed sand-and-grass on the mid-bay flats to harder sand near the reef-side cuts, often within the same day’s fishing. Carrying tan, olive, and one mottled or two-tone pattern covers nearly everything you’ll see.
Sizing a Permit Crab Fly
Permit eat crab flies anywhere from a dime-sized #8 up to a silver-dollar #1/0, but #4 covers more situations than any other single size — it’s the one to over-pack if you’re only bringing a handful. Go smaller (#6) for calm, clear water and fish that have already been shown a few flies that week. Go bigger (#2) in wind, chop, or when you’re specifically working larger, more aggressive fish.
What Our Guides Tie for Chetumal Bay
A dozen flies covers most weeks here: a mix of tan and olive Merkins in #4 and #6, a couple of heavier Bauer Crabs or similar for the deeper bay flats, a few light bead-chain patterns for skinny lagoon water, and (if you’re fishing April or May) several of Tommy’s Floating Crabs for the sargassum mats. That range, more than any single “best” fly, is what actually covers a week of fishing water this varied.
Permit Crab Fly FAQ
What is a permit crab fly? A permit crab fly is any fly pattern designed to imitate a crab, the primary forage for permit on the flats. The category includes patterns like Del’s Merkin, Strong Arm Merkin, Raghead Crab, Bauer Crab, and Avalon, all built to sink quickly, sit naturally on the bottom, and survive a permit’s initial take.
What’s the best all-around permit crab fly? Del’s Merkin in tan, size #4, with medium lead eyes, covers the widest range of permit water and has more confirmed fish to its name than any other pattern. It’s a reasonable choice if you can only carry one crab fly.
What size crab fly should I use for permit? Size #4 is the most versatile choice for most flats fishing. Downsize to #6 for calm, clear conditions and pressured fish; upsize to #2 for wind, chop, or larger fish.
Do permit prefer crab flies or shrimp flies? Crab patterns are the standard first choice across most Yucatan permit water, including Chetumal Bay, and that’s what our guides reach for first. Shrimp patterns can be a useful complement, particularly over the softer mud bottoms found in some of the bay’s backwater lagoons; worth having a few on hand, but not a replacement for a solid crab fly selection.