Mop Flies and Trash Flies: The Dirty Secret to Catching More Trout

Discover why mop flies and other so-called "trash flies" are the most effective tools in your fly box — and how to fish them like a pro.

What Are Trash Flies?

Trash flies are high-odds, fish-catching patterns tied from unconventional materials. Originally dismissed by purists, flies like the Mop Fly, San Juan Worm, Nuke Egg, and Sow Bug have become staples in the boxes of guides, beginners, and tournament anglers alike. What do they have in common? They work — especially when nothing else does.

These patterns imitate common food sources: aquatic worms, caddis larvae, fish eggs, or freshwater crustaceans. They're easy to tie, easy to fish, and hard for trout to ignore.

Why Mop Flies Deserve a Spot in Your Box

Of all the trash flies, mop flies are the most polarizing — and the most deadly. Tied from microfiber mop material (yes, like the cleaning kind), these flies imitate cranefly larvae, caddis pupae, or simply a buggy chunk of calories drifting in the current.

Mop flies perform best in the following situations:

• Post-runoff conditions when water is slightly stained and fish are looking for large, slow-moving meals.
• Cold weather when fish hug the bottom and aren’t willing to chase.
• High-pressure tailwaters where subtle twitching or bounce presentations can trigger curiosity and aggression.

Best colors:

• Chartreuse, tan, and cream for natural clarity.
• Orange and pink as attractors during high water or spawning seasons.

The Other Trash Flies That Matter

San Juan Worms

A classic made from chenille, this fly imitates aquatic worms. Deadly after rainstorms or on rivers with fertile silt bottoms.

Nuke Eggs

Designed to imitate trout and salmon eggs, nuke eggs are excellent during and after the spawn. Use in tailwaters, near redds (but don’t target active spawners), or downstream where egg drifts naturally occur.

Sow Bugs

Mimicking small crustaceans like scuds or freshwater shrimp, sow bugs are a go-to on spring creeks and tailwaters with lots of aquatic vegetation.

Advanced Trash Fly Fishing Tips

Fishing trash flies isn’t just about chucking and ducking. These flies shine when paired with intentional technique:

• Presentation: Let the fly drift naturally. Add subtle twitches or dead drifts through seams and pockets. Mop flies, in particular, work well under indicators or with euro nymph rigs.
• Depth Control: Most trash flies need to be near the bottom. Add split shot, use a tungsten bead, or adjust your indicator until you’re ticking rocks occasionally.
• Fly Line Control: Mending, high-sticking, and tight-line techniques help reduce drag and increase hookups. Especially in clear water, fish demand precision.
• Water Reading: Focus on structure: drop-offs, buckets behind boulders, soft seams next to heavy current. Trash flies work best where trout expect to see a juicy, slow-moving snack.

When to Use Trash Flies

Trash flies can save your day when:

• Hatch-matching fails
• The water is off-color
• You’re guiding someone new
• You're targeting stocked fish
• The pressure’s high and fish are sulking

They’re confidence flies — not subtle, not elegant, but brutally effective.

FAQ: Mop Flies & Trash Flies in Fly Fishing

What is a mop fly in fly fishing?
A mop fly is a popular trout fly made from chenille-like microfiber material that resembles aquatic larvae, such as cranefly or caddis larvae. It's often tied on a jig hook with a bead head to help it sink. Despite its simple look, the mop fly is incredibly effective—especially in off-color water or cold conditions when fish are less active.

Why are they called 'trash flies'?
Trash flies earned their nickname because they're made from unconventional materials like mop heads, chenille, and rubber worm imitations. Some anglers considered them gimmicky or “dirty,” but over time, they’ve proven to catch fish when more traditional patterns fail.

Are mop flies legal in all rivers?
Yes, mop flies are legal in most regulated waters, including artificial-only and fly-fishing-only areas, as long as they are tied in compliance with local regulations (e.g., no bait, barbless hook if required). Always check the local fishing regulations before use.

When should I use a mop fly?
Use mop flies when:

• Water is slightly stained or off-color
• Fish are feeding deep or hugging the bottom
• You’re fishing post-runoff, in cold weather, or early spring
• Traditional patterns aren’t producing

What’s the best way to fish a mop fly?
The best method is under an indicator or with a tight-line nymphing setup. Let the mop fly drift naturally near the bottom. Add split shot or use a tungsten bead if needed to get down quickly. Subtle twitches can also trigger strikes.

What colors of mop flies work best?
Top colors include:

• Chartreuse for stained water
• Tan, cream, or olive in clear conditions
• Orange or pink as attractors, especially near the spawn

Do experienced anglers use trash flies?
Absolutely. Many guides and competition anglers carry mop flies, San Juan worms, and egg patterns as “problem solvers” when fish get picky. They’re not just beginner flies—they’re strategic weapons when conditions get tough.

Can I use trash flies for species other than trout?
Yes. Trash flies can be effective for bass, panfish, and even carp. Worms and eggs work particularly well for warmwater species, and mop flies can trigger strikes from curious or aggressive fish in almost any environment.

Are mop flies good for beginners?
They’re excellent for beginners. Mop flies are easy to fish, highly visible in the water, and often produce fast feedback. For newer anglers learning indicator nymphing, mop flies help build confidence quickly.

How do I tie my own mop flies?
You can tie mop flies with jig hooks, tungsten or brass beads, mop chenille (cut from microfiber cleaning mitts), and a bit of dubbing or hackle for extra movement. They’re fast, cheap, and satisfying to tie—even if you’re just starting out.